particular specification m23: gravity belt thickeners

City of Johannesburg Johannesburg Water SOC Ltd

17 Harrison Street Johannesburg

Johannesburg Water PO Box 61542 Marshalltown 2107

www.johannesburgwater.co.za

Tel +27(0) 11 688 1400 Fax +27(0) 11 688 1528

PARTICULAR SPECIFICATION

M23: GRAVITY BELT THICKENERS

3 2012-07-30 General update and re-issue

2 2010-02-16 General review J Ritchie

1 2009-05-12 Review of Mechanical / Electrical and Control /

Instrumentation Standards, plus New Design Guidance

Rev Date Description Signature:

JW Wastewater Partnership

Signature: Approval

from Johannesburg Water

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City of Johannesburg Johannesburg Water (SOC) Ltd

PARTICULAR SPECIFICATION M24: GRAVITY BELT THICKENERS

CONTENTS

M23.1 SCOPE ................................................................................................................................................ 2

M23.2 INTERPRETATIONS .......................................................................................................................... 2

M23.2.1 Abbreviations .................................................................................................................................... 2

M23.2.2 Standards ........................................................................................................................................... 3

M23.2.3 General Requirements ...................................................................................................................... 3

M23.3 GENERAL ........................................................................................................................................... 3

M23.3.1 General Design Parameters ............................................................................................................. 3

M23.4 SLUDGES TO BE THICKENED ......................................................................................................... 4

M23.5 PROCESS AND DESIGN ................................................................................................................... 4

M23.5.1 Process Description and Design ..................................................................................................... 4

M23.5.2 Equipment Required ......................................................................................................................... 5

M23.6 EQUIPMENT ....................................................................................................................................... 5

M23.6.1 Sludge Holding & Storage Tank Mixing .......................................................................................... 5

M23.6.2 Pumping Equipment ......................................................................................................................... 6

M23.6.3 Automatic Backwash Strainer ......................................................................................................... 8

M23.6.4 Polyelectrolyte Injection and Mixing ............................................................................................... 9

M23.6.5 Gravity Belt Thickeners .................................................................................................................... 9

M23.6.6 Access Structures and Platforms ................................................................................................. 15

M23.6.7 Magnetic Flow Meters ..................................................................................................................... 15

M23.6.8 Solids Density Meters ..................................................................................................................... 15

M23.6.9 Laboratory Equipment .................................................................................................................... 15

M23.7 MATERIALS AND CORROSION PROTECTION ............................................................................ 16

M23.7.1 General ............................................................................................................................................. 16

M23.7.2 Materials of Construction ............................................................................................................... 16

M23.7.3 Corrosion Protection ...................................................................................................................... 17

M23.8 INSTALLATION AND OPERATING REQUIREMENTS .................................................................. 17

M23.8.1 Installation Requirements .............................................................................................................. 17

M23.8.2 Tools ................................................................................................................................................. 18

M23.9 INFORMATION REQUIRED ............................................................................................................. 18

M23.9.1 Manufacturing Drawings ................................................................................................................ 18

M23.9.2 As Built Drawings ........................................................................................................................... 18

M23.10 TESTING/COMMISSIONING ............................................................................................................ 18

M23.10.1 Preliminary Test .............................................................................................................................. 18

M23.10.2 Acceptance Test .............................................................................................................................. 18

M23.11 QUALITY MANAGEMENT ............................................................................................................... 19

M23.12 MEASUREMENT AND PAYMENT................................................................................................... 19

M23.12.1 General ............................................................................................................................................. 19

M23.12.2 Testing .............................................................................................................................................. 20

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M23.1 SCOPE

This Specification covers the design parameters, manufacture, supply, installation, testing and commissioning of equipment for sludge dewatering by linear screen/s as follows:-

(a) Mixing equipment for the sludge storage tank/s.

(b) Sludge pumping equipment.

(c) Gravity Belt Thickeners

(d) Effluent wash water pumps.

(e) Support and access structural steelwork.

(f) Associated pipework, valves, strainers and polymer injection device/s etc.

(g) Ancillary equipment. (air compressor equipment or hydraulic equipment).

(h) Sludge pumping equipment for thickened sludge.

(i) Electrical switch gear, cabling and instrumentation (if specified).

Coagulation chemical (polyelectrolyte) preparation and dosing equipment will be the subject of another specification and is not covered in this specification. However the control of the dosing will be closely interfaced with the above equipment, and the necessary instrumentation will be required to also measure, record and control the dosing equipment.

This specification shall not apply to filter belt press machines, which may follow gravity belt thickeners to achieve greater sludge dewatering. Filter belt presses will be the subject of a separate specification. However, if applicable, the operation and control of each filter belt press machine will be closely linked with the above equipment, and the necessary machinery and instrumentation shall be provided to also interface with the filter belt press equipment.

This Specification shall be read in conjunction with the Project Specific Specification. Clarifications to this specification are set out in the Project Specific Specification, which shall precede this specification in the Contract Document.

M23.2 INTERPRETATIONS

The following Interpretations relating to this specification, shall form part of the Contract Document:

M23.2.1 Abbreviations

In this Specification the following abbreviations will apply:-

ANSI : American National Standards Institute

ASTM : American Society for Testing and Materials

BS : British Standards Institution

SANS : South African National Standards

SIS : Swedish Institute of Standards

DIN : Deutsch Industry Normen

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ISO : International Organisation for Standardization

ASME : American Society of Mechanical Engineers

SAECC : South African Electrolytic Corrosion Committee

AGMA : American Gear Manufactures Association

M23.2.2 Standards

All design standards for the dosing of chemicals shall be subject to the latest amendments and editions of the following standard specifications:-

BS 5304 : Code of practice for safeguarding of machinery

M23.2.3 General Requirements

This specification shall be read in conjunction with the following specifications:-

M20: Particular Specification for Valves

M21: Particular Specification for Pressure Pipework

M18: Standard Specification for Centrifugal Type Pumps

G01: Particular Specification for Colour Codes

G02: Particular Specification for Corrosion Protection

Automation and Control Design Standards Volume 8: Flow Measurement

Automation and Control Design Standards Volume 9: Level Measurement

Automation and Control Design Standards Volume 20: Density Measurement

M23.3 GENERAL

M23.3.1 General Design Parameters

The following requirements shall be met:-

(a) The equipment shall be designed to facilitate efficient manufacture, inspection, transportation, installation, maintenance, cleaning and repairs.

(b) The equipment shall be designed to ensure safe and satisfactory operation for a life expectancy of at least 12 years under the conditions prevailing at the Site.

(c) The equipment shall be designed to prevent undue stresses being produced by expansion and contraction due to temperature change, and other local natural and manmade conditions.

(d) The equipment shall be designed to keep maintenance costs to a minimum.

(e) The equipment shall comply with the legal requirements in respect of safety and the prevention of environmental pollution.

(f) The equipment shall satisfy any specific requirement contained in the relevant statutory codes and legislation.

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(g) The equipment shall be suitable for operation 365 days per year, 24 hours per day under the specified design conditions.

(h) All equipment shall be provided to provide a fully operational plant within the scope of the Contract.

(i) All materials from which the equipment is manufactured shall be compatible with the chemicals used and suitable for the intended duty and service conditions.

(j) All equipment shall be suitably treated and protected from corrosion and erosion.

(k) After approval by the Engineer, at the time of the award of the Contract, the information stated in the Data Sheets shall be fully complied with.

(l) All electrical equipment, forming part of the specified equipment, shall be sealed against penetration by the spray belt cleaning water in use, which may be in aerosol form, and be also accessible for repair and maintenance.

M23.4 SLUDGES TO BE THICKENED

The source and type of sludge/s to be thickened, together with its / their analysis, characteristics, and dry solids concentration, shall be as indicated in the Project Specific Specification.

M23.5 PROCESS AND DESIGN

M23.5.1 Process Description and Design

The following basic steps shall be followed for the dewatering of sludge using linear belt type dewatering screens.

(a) Treat the sludge with a chemical to coagulate the sludge particles.

(b) Handle the coagulated sludge gently to avoid break up of the coagulated particles.

(c) Thicken the sludge on a moving mesh belt under gravity.

Special attention shall be given to the mesh of the belts, the speed of the belts and the positioning of ploughs in the gravity dewatering zone.

The equipment shall be capable of thickening the sludge/s specified in the Scope of Works, and shall be designed and selected by the Contractor to achieve the thickened sludge dry solids concentration, solids recovery and polyelectrolyte consumption as specified in the Scope of Works.

Flocculent dosing must not exceed 1.0 kg per ton of dry solids. The gravity belt filter press unit shall have an effective belt width of 2.5 m.

The dewatering installation is depicted on the Process and Instrumentation Diagram and the Site Layout Drawings provided. The installation comprises the following major units:

(a) Sludge storage tanks and mixers.

(b) Sludge feed pumps.

(c) Polyelectrolyte dosing equipment.

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(d) Gravity Belt Thickeners.

(e) Thickened sludge pumps.

(f) Service water tank and pumps for the supply of wash water.

(g) Air compressing equipment (if applicable).

M23.5.2 Equipment Required

The equipment to be provided shall comprise the following, unless otherwise indicated in the Scope of Works:

(a) Mixing equipment for mixing the contents of the sludge storage tank(s)

(b) Sludge feed pumping equipment

(c) Gravity Belt Thickeners.

(d) Access platform steelwork.

(e) Service water pumps and automatic backwash inline strainer.

(f) Thickened sludge pumps.

(g) Associated piping, valves and fittings

(h) Air compressing equipment (or alternatively i)

(i) Hydraulic power pack equipment.

(j) Electrical switchgear, cabling and instrumentation.

(k) Solids Meter.

(l) Ultrasonic level measuring and control equipment for the sludge storage tank/s.

(m) Solids density meter to measure the concentration of feed sludge to the thickening equipment.

(n) Solids density meter/s to measure the concentration of thickened sludge from the sludge thickening equipment.

M23.6 EQUIPMENT

M23.6.1 Sludge Holding & Storage Tank Mixing

Sludge from the physical and / or biological treatment process will be delivered to the concrete sludge storage tank/s. The type, solids concentration and characteristics of the sludge/s shall be as specified in the Scope of Works. The volume, operating levels and dimensions of the sludge holding tank are also given in the Scope of Works, and as shown on the relevant drawings.

The sludge contents of the tank(s) shall be mixed by means of vertical shaft mixers.

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M23.6.1.1 Mechanical Mixers

Vertical shaft mixers shall be selected in preference to submersible mixers unless the tank/s geometry will not allow effective mixing by vertical type units.

The design, number and location of the vertical shaft or submersible mixers shall be suitably selected to achieve a uniform solids concentration of the tank sludge contents and avoid the deposition of grit and solid particles. Cognisance shall be taken of the nature of the sludge being stored.

Not withstanding the above the minimum energy density imparted to the sludge by the mixers shall be 15 w/m3.

The equipment supplied shall comprise:

(a) Mechanical mixers complete with motors and any necessary speed reducers etc.

(b) All necessary mounting bridges, base plates, guides, hoists and fixings etc.

(c) Ultrasonic level meter and transmitting equipment for each tank.

M23.6.2 Pumping Equipment

M23.6.2.1 Sludge Feed Pumps

The sludge feed pumps shall pump sludge from the storage tanks to the dewatering units. They shall have variable speed drives and be capable of pumping sludge of the characteristics, quantity and pumping head as defined in the Scope of Works.

The pumps shall be either:

(a) Of the centrifugal, end suction or immersible type in accordance with specification M18: Standard Specification for Centrifugal Type Pumps. Submersible pumps situated in the storage tanks will not be acceptable.

(b) Of the Positive Displacement Type.

Piping shall be 304 stainless steel in accordance with the requirements of specification M21: Particular Specification for Pressure Pipework.

Corrosion protection shall be in accordance with specification G02: Particular Specification for Corrosion Protection.

Isolating valves shall be manually operated, flanged resilient seal valves

Non return valves shall be of the flanged, swing check type with external levers and counter weights.

The pumps shall draw sludge from the sludge storage tank/s and discharge directly to the dewatering units. A single pump shall deliver to each dewatering unit and a common standby unit shall be supplied. The number of pumps shall be as indicated in the Scope of Works. The operation of the system shall be automatically controlled as described in the Control Philosophy.

The equipment required shall comprise the following:

(a) Sludge pumps with fixed speed drives, one duty and one standby as described in the Scope of Works.

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(b) A magnetic flow meter for each of the sludge delivery lines to each dewatering unit.

(c) All suction and delivery piping, valves, pressure gauges and fittings to draw from the sludge holding tank/s and deliver to the dewatering units.

M23.6.2.2 Service Water Pumps

Service water required as wash water for washing the belts of the linear screen shall be provided in one of the following ways, as indicated in the Scope of Works.

(a) From the existing potable water supply.

(b) From the existing pressurised effluent water system.

(c) From new final effluent pumps and a strainer which shall be provided under this Contract. These pumps shall be of the centrifugal type in accordance with specification M18: Standard Specification for Centrifugal Type Pumps.

When new pumps are to be provided, final effluent shall be used as wash water. The pumps shall draw from the final effluent storage tank or channel. They shall be capable of the following duty and selected in the following manner:

(a) There shall be two pumps one duty and one standby pump to serve all the GBT’s.

(b) The above pumps shall pump into a common discharge manifold, from where a strainer shall be fitted and a supply line to each thickening unit shall branch off. A recycle line shall be provided to recycle excess flow back from the common manifold to the effluent storage tank. The recycle line shall be fitted with an adjustable pressure relief valve that can be set in the range 6.0 to 7.5 Bar to deliver at least 50% of the capacity of one pump at 7.0 Bar head.

(c) Each pump shall be rated at least 7.0 Bar pressure and have a minimum discharge rate as specified in the Scope of Works, or as determined by the thickening unit supplier.

(d) Notwithstanding the above, each pump shall be rated with a sufficient pressure and discharge quantity for the belt washing of one dewatering unit plus 10%.

(e) When specified in the Project Specific Specification, these pumps shall also be used for the additional duty of providing spray cleaning water for preceding filter belt presses and / or make up water and dilution water for the associated polyelectrolyte dosing system.

The equipment associated with the wash water pumps supplied shall comprise:

(a) Identical pumps as specified.

(b) Suction and delivery piping, valves and fittings from the outlet of the effluent tank to the specified points of delivery.

(c) Bypass piping and pressure relief valve from the common manifold.

(d) An automatically operated isolating valve on each pipeline to each dewatering unit.

(e) A pressure reducing valve to reduce the pressure from the spray water delivery pressure, to a pressure suitable for use as polyelectrolyte make up and dilution water (if applicable).

(f) Ultrasonic level meter fitted to the effluent storage tank or channel.

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Piping shall be steel in accordance with the requirements of specification M21: Particular Specification for Pressure Pipework. Corrosion protection shall be in accordance with specification G02: Particular Specification for Corrosion Protection.

All isolating valves shall be knife gate valves.

M23.6.2.3 Thickened Sludge Pumps

The thickened sludge pumps shall pump sludge from the thickened sludge collection tank to the disposal point as indicated in the Scope of Works. They shall have variable frequency speed drives and be capable of pumping sludge of the dry solids concentration and viscosity expected from the dewatering units, at the pumping rates and at the pumping head as defined in the Scope of Works.

The pumps shall be of the Progressive Cavity Helix sludge type.

Piping shall be steel in accordance with the requirements of specification M21: Particular Specification for Pressure Pipework.

Corrosion protection shall be in accordance with specification G02: Particular Specification for Corrosion Protection.

Isolating valves shall be manually operated, flanged resilient seal valves

Non return valves shall be of the flanged, swing check type with external levers and counter weights.

The equipment associated with the sludge pumps shall comprise the following:

(a) Sludge pumps with variable speed drives, one for each thickening unit together with a common standby unit.

(b) A magnetic flow meter for each of the sludge delivery lines from each thickening unit.

(c) All suction and delivery piping, valves, pressure gauges and fittings to draw from the sludge collection tank/s and deliver to the disposal point/s.

M23.6.3 Automatic Backwash Strainer

An automatic backwash strainer shall be provided when final effluent is to be used for spray washing purposes.

The inline strainer shall be installed at the end of the common manifold of the delivery line from the service water pumps, such that all the thickening units are protected. The strainer shall be of the automatic self cleaning type. The backwash or cleaning process may be continuous or intermittent. If intermittent cleaning is provided the cleaning process shall be initiated when the differential pressure across the strainer is 5 m or after 3 hours whichever is the sooner.

The cleaning process shall be by means of a reverse flow of water through the strainer basket. Cross flow cleaning not be acceptable.

The back wash water valves shall be electrically actuated and motors shall be 3 – phase.

The strainer shall be sized to handle a flow 25% in excess of the maximum required process flow at a head 50% higher than the specified working pressure.

The strainer shall be of the wedge wire type and have an aperture of 200 microns.

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All back wash water pipework shall be provided to the designated disposal point.

M23.6.4 Polyelectrolyte Injection and Mixing

Polyelectrolyte, after dilution shall be intimately mixed into the sludge feed to each dewatering unit. The polyelectrolyte shall be introduced into the flow at a minimum of 6 points located radially on the circumference of the sludge feed pipe. Sufficient turbulence shall be created in the flow downstream of the dosing point to create thorough mixing, be means of an in-line mixer manufactured in stainless steel.

M23.6.5 Gravity Belt Thickeners

M23.6.5.1 General

Gravity Belt Thickeners are required to thicken the sludge and to achieve the performance requirements as set out in the Project Specific Specification.

The gravity belt thickeners shall be of the continuous belt gravity drainage type specifically designed for use with sewage sludge’s and low polyelectrolyte consumption.

Each Gravity Belt Thickeners shall incorporate the following basic elements:

(a) A screen framework.

(b) A flocculation chamber

(c) A feed chute.

(d) A series of belt rollers.

(e) A filter belt.

(f) A series of belt support members.

(g) A series of sludge ploughs.

(h) A belt discharge scraper.

(i) A drive unit.

(j) A belt tensioning system.

(k) A belt tracking system.

(l) A belt washing system.

(m) A wash water collection and drainage system.

(n) A filtrate collection and drainage system.

(o) All necessary top and side closures and guards.

(p) All necessary electrical and ancillary equipment.

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The screen shall be designed and selected such that the maximum loading rates shall not exceed the following criteria:

Type of sludge

Gravity Belt Thickeners

Hydraulic Loading Dry Solids Loading

m3/h/m effective width of belt Kg/h/m effective belt width

Digested primary 35 400

Raw primary 35 500

Waste activated 35 250

M23.6.5.2 Framework

The framework of the Gravity Belt Thickener shall be a Stainless Steel, robust, heavy duty assembly, to suit the particular operating environment.

The structural members of the framework shall be of rolled stainless steel sections or machine press formed sections designed as a completely welded or both welded and bolted construction in such a way as to provide maximum strength and rigidity. No stainless steel section shall be less than 4.5 mm thick. It shall be so designed that rollers can be removed from the side or end of the frame with minimum disturbance to other roller assemblies or components.

The design of the frame shall be based on a minimum belt tension of 5,000 N/m width of belt. The design of the load bearing structural members shall be such as to ensure a maximum deflection of L/2,000 where L is the span length. The maximum stress in structural elements shall not exceed one fifth of the yield stress of the particular material.

The frame shall be so designed and fabricated that no twisting can take place, and roller alignment is maintained by the frame geometry during lifting and transportation: The frame rigidity shall be such that during operation no external support shall be required.

The frame shall also be designed so that large, easily removable enclosures can be provided to prevent splashing, aerosol and spray discharge from the units whilst allowing easy access for cleaning and maintenance.

M23.6.5.3 Flocculation Chamber

A flocculation chamber for each dewatering unit shall be provided prior to discharge of the sludge onto the linear screen. The chamber shall provide sufficient retention to complete flocculation before the sludge is discharged onto the screen belt. The contents of the chamber shall be mixed by means of a slow speed low shear vertical shaft mixer fitted with a manually adjustable reduction gearbox. The mixing arrangement shall ensure that the entire contents of the chamber are uniformly agitated and shall prevent short-circuiting of sludge. Flocculation chambers without mechanical agitation, in which settled sludge solids may accumulate will not be acceptable.

The flocculation chamber shall be attached to, or form part of the dewatering unit.

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M23.6.5.4 Feed Chute

A stainless steel feed chute shall be provided to distribute sludge evenly from the flocculation chamber over the width of the screen belt in such a manner as to avoid excessive turbulence and consequent floc break-up. The distribution mechanism shall be so arranged that the maximum static head loss between the top water level in the flocculation tank and the linear screen shall not exceed 75 mm.

The sloping chute shall incorporate division plates in a fan formation to ensure that distribution onto the belt is equal and that stationary clumps of sludge cannot form on the chute. Alternatively the sludge may be evenly distributed by means of a rotary spreader screw, which spans the width of the screen and which incorporates opposite hand helixes, which distribute the sludge out from the centre over the width of the belt, but not allow sludge to spill over the edges of the belt.

M23.6.5.5 Rollers & Drums

The cylindrical bodies of all rollers and drums shall be manufactured from steel tube with dimensions to ANSI B 36.10 and have a wall thickness of at least Schedule 40.

Stub shafts shall be manufactured from low carbon steel bar. The bar diameter shall used shall be at least twice the stub shaft diameter before machining. Mechanical notches shall be avoided by using smooth and large radii at the knuckle.

Flanges shall be manufactured from carbon steel plate.

Welding shall be full penetration and shall not take place at high stress points. Metallurgical notches shall be avoided and the welded roller assembly shall be fully stress relieved prior to machining.

All rollers and drums shall be machined on the cylindrical outer surface truly concentric with the stub shafts.

All stub shaft flanges and roller tubes which are subject to stress reversal, shall be designed with a stress no greater than 75 Mpa.

All rollers and shafts shall be coated with 'Rilsan' or equal thermo plastic polymer material of thickness not less than l.0 mm up to the bearing housings.

Drive rollers and drums shall be coated with a layer of reinforced Neoprene rubber of thickness not less than 5 mm. This shall be applied to the roller surface and be machined to provide a true face after manufacture.

M23.6.5.6 Bearings and Lubrication

All bearings shall be of the double row spherical roller type and be rated for a minimum L.10 life of 500 000 hours. The bearings shall fit to the shaft with the use of a tapered adapter sleeve. Housings shall be of the split plumber block type with provision for one or two locating rings. The locating ring/s shall only be installed in one of the rollers bearings so that thermal expansion of the relevant roller can be taken up in the housing at the opposite end.

Seals shall be suitable for the environment in which they will operate and be resistant to high pressure washing. A waterproof bearing cover shall be installed on the outer side of each bearing (except on the drive shaft) and an additional labyrinth contact type seal, preferably spring loaded, shall be provided to give further protection on the inner side.

All bearings and seals shall be easily replaceable from the outside of the machine.

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All bearings shall be lubrication from a common greasing station using an automatic progressive lubricator. The lubricator shall be of the ‘Woerner’ or equivalent type such that all grease lines are progressively provided with metered amount of grease. Lubricators based only on a common equal pressure to all grease lines will not be acceptable. The lubricator shall be programmed to start and stop when the screen belt stops and starts.

All grease piping and fittings to stationary bearings shall be stainless steel. Movable bearings such as on the tracking and tensioning rollers shall incorporate a short flexible grease pipe braided with stainless steel.

Bearings or other tracking and tensioning mechanical or electrical equipment, shall not be located inside the enclosure in the wetted area of the dewatering unit.

(a) Bearing selection

Bearings for drive, idle and press rollers shall be able to accommodate a misalignment of up to 3 degrees included angle without reduction in capacity. All bearing components shall be stock metric sizes readily available from local distributors and suppliers. A full list of bearings with identification type numbers shall be provided.

(b) Bearing selection data

Bearing selection data showing the method of calculating L10 bearing life, and detailing methods of calculating bearing loads shall be submitted on request.

Bearings shall be selected using maximum operating speeds, and a belt tension of 10 Kg/cm belt width in each belt. Calculations shall also allow for roller self-weight and drive torque.

M23.6.5.7 Screen Belt

The screen belt shall be manufactured from high permeability durable woven monofilament polyester fibre selected to meet the duty requirements with a guaranteed operational life before replacement of not less than 10,000 hours continuous running.

The aperture size shall be selected to meet the specified performance and should not exceed 600 micron in either direction.

The belt shall be joined by an approved clipper seam using high tensile steel cable bonded with resin and incorporating a chevron or similar stabilising seam. Belt edges shall be heat sealed and bonded for stability. All metallic parts of the belt joint seam shall be stainless steel.

Spillage of sludge over the sides of the belt shall be prevented either by the provision of side skirting or by the chamfering (dishing) of the cloth surface at each side of the drainage zone.

M23.6.5.8 Belt Support Members

The top side of the belt shall be kept truly flat (except at the sides where chamfers may be incorporated to prevent spillage of the liquid) to ensure that the ploughs are in contact with the belt at all times. This may be achieved either with rollers, or by easily replaceable engineering plastic slider bars, both in conjunction with the belt tension. Slider members if used shall be guaranteed for a life of at least 10,000 hours continuous running.

M23.6.5.9 Plough System

Ploughs, which are hinged, or, which slide vertically in individual guides, shall be incorporated to rest on, and be in light contact with the belt to move the sludge in such a way that the belt does not blind with solids and provide efficient drainage. The ploughs shall prevent the sludge from

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flowing off the side of the belt.

They shall "plough" the sludge blanket so that the maximum degree of free drainage is achieved prior to discharge.

The sludge ploughs shall be so designed as to facilitate adjustment by the operator in safety and comfort for optimum drainage. It shall be possible to remove the ploughs from the sludge blanket if considered necessary during operation. A minimum of six rows of ploughs shall be provided.

M23.6.5.10 Discharge Scraper & Chute

A stainless steel discharge scraper and chute shall be provided to remove the sludge from the belt at the discharge end and evenly distribute the thickened sludge onto the next thickening stage or to disposal. The scraper shall be such that no sludge can pass between the scraper and the belt, and is easily adjustable with an easily replaceable wearing edge.

M23.6.5.11 Geared Motor Drive

The belt shall be driven through a geared motor speed reducer drive incorporating helical and / or bevel gears. Easily removable shaft mounted units are preferred so that radial bearing loads are minimised. Geared motors shall be selected from a standard range.

The ISO power rating of the gearbox shall be not less than 2.00 on the installed motor power or 2,25 on the absorbed power, which ever is the greater.

Gears shall be of the helical or bevel type manufactured from the highest quality alloy steel, gas carburized and accurately ground.

The transmission mechanism shall be totally enclosed, oil tight, and oil or grease lubricated.

The geared motor shall be positioned such that the oil can be easily drained and re-filled.

Speed variation shall be by means of a variable frequency inverter located in the dewatering unit control panel of the Motor Control Centre.

The belt shall be able to operate at a speed of between 6.0 m/min. and 30.0 m/min. Should this not be possible with a frequency converter, then a mechanical variator should also be supplied on each gearbox.

The overall efficiency of the gearbox and final drive arrangement shall be in excess of 90%.

M23.6.5.12 Filtrate Collection Pans

Separate Pans shall be provided for the collection of filtrate and wash-water from the screen, with piping to allow separate disposal if required. Collection, wash water pans and pipe work shall be manufactured in stainless steel.

M23.6.5.13 Wash Water System

A thickening belt spray wash system complete with pipework, nozzles and valves etc. shall ensure that the belt is cleaned free of all solids on the return run. The spray bar and nozzles shall be fitted with a manual brush cleaning. This shall be readily accessible from the access walkway.

The Contractor shall provide all the necessary interconnecting wash-water pipework, pressure reducing valves, isolating and control valves and supports to connect to the washwater supply systems.

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M23.6.5.14 Belt Tracking

The tracking of the belt shall be accomplished by the longitudinal movement at one side of a tracking roller, which has a shallow angle of wrap on the return side of the belt. The movement of the roller shall be achieved by moving, within limits, one roller shaft bearing housing within linear guides. The motive force for movement shall be by an actuator, either of the mechanical / electrical type.

Belt tracking system shall be provided to control belt alignment under all operational conditions. One belt edge shall run against a paddle switch, which shall be provided with a ceramic face. This paddle switch shall send a signal to move the roller end and bearing in the relevant direction to correct belt alignment.

The belt tracking system shall be of the type which anticipates belt movement and takes corrective action proportional to belt drift. A pair of sensors for each belt shall be provided to sense a shutdown misalignment condition.

The control logic shall prevent nuisance shutdown from occasional activation of these sensors. The sensor shall be used to initiate an alarm in the control panel.

The control mechanism shall not require either excessive belt wrap angles around the guide roller, or excessive slew travel, which would lead to belt deformation and wear.

The linear guides for the moving bearing housing shall be provided with low-friction tracks.

M23.6.5.15 Belt Tensioning

An automatic belt tensioning system shall be provided to maintain the belt tension at the required constant load regardless of sludge loading and belt stretch, and also to accommodate different length replacement belts.

Belt tensioning shall be accomplished by the longitudinal movement at both sides of an end roller. The movement of the roller shall be achieved by moving, equally and within limits, both roller shaft bearings within linear guides. The motive force for movement shall be mechanical / electrical. Belt tensioning systems utilizing springs shall not be acceptable.

It shall be possible to read from a pressure gauge, or load cell, the tension (kN) in any belt at any time.

M23.6.5.16 Inspection Enclosures Panels

The thickening unit shall be designed and constructed in such a way as to provide maximum protection for operations staff against injury from moving machinery, and harm to health from the bio-hazards present in air borne particles from sprays containing sewage sludge.

All Gravity Belt Thickeners shall be enclosed at the top, sides and ends to minimise the creation of airborne mists from the cleaning sprays. Protection shall be provided against the egress of spray or spillage and against accidental contact with rolling assemblies during operation, by the provision of large easily removable panels in the enclosures.

The enclosure panels shall be easily removable by operations staff to allow full access for inspection and cleaning purposes. It shall be possible to operate the machine with the enclosure panels removed.

M23.6.5.17 Guards

In addition to the requirements relating to the enclosure panels and the requirements of the Occupational Health and Safety Act, all drives and pinch zones between belts and rollers shall

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be fully enclosed with a robust guard manufactured from expanded steel mesh. The guards shall be provided with a robust frame and hinge arrangement to permit free access to equipment for maintenance and repairs.

M23.6.5.18 Odour control

The Gravity Belt Thickening unit shall be designed and constructed in such a way as to provide maximum protection for operations staff against injury to health from the bio-hazards present in sewage sludge.

Not withstanding the above, when primary sludge is to be thickened, a top enclosure or hood with suitable air extraction points shall be provided for the press for the extraction of foul gases. A forced ventilation system shall be provided so that all gases can be ventilated through the roof of the building.

M23.6.6 Access Structures and Platforms

Support and access structures, stairs and walkways shall provide access to the Gravity Belt Thickeners and drive, flocculation chamber and mixer and provide access to all other equipment.

The access structure shall allow for access to each Gravity Belt Thickener and to all mechanical components. The structure shall be elevated at a level which will provide an unrestricted view across the full width of the unit and the material on the linear screen feed zone and which will allow at least 2,0 m free walking height underneath.

The support and access structure shall be robustly constructed from steel sections. Access walkways and staircases shall not be less than 750 mm wide and shall be equipped with kick plates.

Stair cases shall have an angle of not more than 350 to the horizontal, with at least 300 mm wide treads, and not more than 200 mm equally spaced risers. All necessary hand railing shall be provided. The walkways shall form one complete interconnected system. Direct access to the polyelectrolyte dosing area shall be included.

Access platforms shall allow adequate safe access, as required in terms of the OHS Act shall be provided for operation and maintenance of the equipment. The extent of the access platforms and ancillaries is shown on the drawings.

M23.6.7 Magnetic Flow Meters

Magnetic flow meters shall be in accordance with the Automation and Control Design Standards Volume 8: Flow Measurement

M23.6.8 Solids Density Meters

The sludge density meter shall comply with The Automation and Control Design Standards Volume 20: Density Measurement.

M23.6.9 Laboratory Equipment

When so indicated in the Project Specific Specification the Contractor shall supply an infrared balance capable of measuring the percentage total dry solids concentration of the thickened sludge to within 2 % of the total dry solids concentration.

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M23.7 MATERIALS AND CORROSION PROTECTION

M23.7.1 General

The Gravity Belt Thickening units will e operating in very corrosive environment and where possible all components are to be manufactured in stainless steel.

No fabricated mild steel components shall have a thickness of less than 5.0 mm.

No fabricated 3CR12 components shall have a thickness of less than 4.5 mm.

No fabricated 304 stainless steel components shall have a thickness of less than 2.0 mm.

No fabricated 316 stainless steel components shall have a thickness of less than 1.6 mm.

All components fabricated in 3CR12 or stainless steel shall be pickled and passivated in accordance with the requirements of Particular Specification G02: Corrosion Protection.

Components fabricated in stainless steel shall be lightly sandblasted too provide a uniform, attractive external surface finish.

No exposed galvanised components shall be used inside the wetted area of the dewatering unit.

Where stainless steel bolts are used, suitable anti-seize compound shall be applied to aid subsequent removal.

M23.7.2 Materials of Construction

M23.8.2.1 Mixers for Sludge Holding Tank

Mixer Support Steelwork .............................................................. SABS 1431 Grade 300WA Steel

Mixer Shaft ....................................................................................................... 304 Stainless Steel.

Impeller ....................................................................................................................... Carbon Steel

Guides, Hoists and Fittings (if applicable.) ....................................................... 304 Stainless Steel

Fasteners and Concrete Anchors ..................................................................... 316 Stainless Steel

M23.8.2.2 Sludge Feed Pumps

Pipework ........................................................................................................... 304 Stainless Steel

Puddle Pipes ..................................................................................................... 304 Stainless Steel

General Steelwork ............................................................................................ 304 Stainless Steel


M23.8.2.3 Gravity Belt Thickeners

Framework ........................................................................................................ 304 Stainless Steel

Flocculation Chamber ....................................................................................... 316 Stainless Steel

Flocculation Mixer Shaft & Impeller .................................................................. 316 Stainless Steel

Feed Chute ....................................................................................................... 304 Stainless Steel

Enclosure Steelwork and Guards ..................................................................... 304 Stainless Steel

Associated Pipework ......................................................................................... 304 Stainless Steel

Roller Tubing ...................................................................................... ASTM A106 Seamless Steel

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Roller Stub Shafts and Flanges ................................................... SANS 1431 Grade 300WA Steel

Ploughs ............................................................................................................. Engineering Plastic

Belt seam components ..................................................................................... 316 Stainless Steel

Belt Scrapers ..................................................................................................... Engineering Plastic

Filtrate and Wash Water Pans .......................................................................... 316 Stainless Steel

Any other steel Components ............................................................................. 304 Stainless Steel


M23.8.2.4 Access Platform Steelwork

Steelwork ..................................................................................... SANS 1431 Grade 300WA Steel

Walkway Gratings ........................................................................ SANS 1431 Grade 300WA Steel

Stair Treads .................................................................................. SANS 1431 Grade 300WA Steel

Hand Railing ...................................................................................................... 304 Stainless Steel


M23.8.2.5 Service Water Pumps

Pipework up to 150 DN ....................................................... Carbon Steel to SANS 62 Heavy Wall

Pipework over 150 DN .................................................. Carbon Steel to ASTM A106 Schedule 40

Backwash Strainer Body ............................................................................................. Carbon Steel

Backwash Strainer Filter Element ..................................................................... 316 Stainless Steel

General Steelwork ................................................. SANS 1431 Grade 300WA Steel or equivalent


M23.8.2.6 Thickened Sludge Pumps

Pipework ........................................................................................................... 304 Stainless Steel

Puddle Pipes ..................................................................................................... 304 Stainless Steel

General Steelwork ....................................................................... SABS 1431 Grade 300WA Steel


M23.7.3 Corrosion Protection

Corrosion protection shall be carried out in accordance with the requirements of G02: Particular Specification for Corrosion Protection

M23.8 INSTALLATION AND OPERATING REQUIREMENTS

M23.8.1 Installation Requirements

The installation shall comply with the following requirements:

M23.8.2.1 Pump Units, Pipes and Fittings

Pumps and motors shall be mounted on a common base plate, which shall be mounted on a pump plinth raised at least 150 mm above the general floor level. The plinth shall be cast by others to the Contractors requirements. The base plate shall be accurately levelled by the Contractor and firmly anchored to the pump plinth. All pipework shall be accurately levelled and

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fully supported and incorporate flexible couplings to ensure that no load or stress is imparted to the pumps or other mechanical items.

Pipework within the buildings shall be located above floor level at a sufficient height to enable wash down and sweeping of the area and to allow for ready access for repair and maintenance.

M23.8.2 Tools

A wall mounted toolbox shall be provided and mounted as directed by the Engineer. It shall contain all tools required to service and maintain all the equipment provided.

M23.9 INFORMATION REQUIRED

M23.9.1 Manufacturing Drawings

The Contractor shall inform the Engineer prior to the manufacture of any piece of equipment of the availability of the relevant completed general arrangement drawings for inspection and approval by the Engineer to be made available at the Engineer’s office. The Contract will be deemed incomplete until the Contractor has made available these drawings to the Engineer, and they have been checked and approved.

M23.9.2 As Built Drawings

The Contractor shall provide ‘To Scale’ as built General Arrangement Drawings of all the relevant equipment. Such drawings shall be made available in a recognized electronic format such as AutoCAD.

M23.10 TESTING/COMMISSIONING

Two series of tests shall be conducted on the equipment, as specified hereunder.

M23.10.1 Preliminary Test

Before delivery of the Gravity Belt Thickening equipment is accepted, the thickening assembly shall be dry tested, at the supplier's works, throughout the design speed and belt tension range. Test certificates shall be issued to demonstrate compliance with the specification.

M23.10.2 Acceptance Test

General

After installation of the equipment and before commissioning, each item of mechanised equipment shall be tested throughout its operating range and calibration curves shall be produced. The calibration curves shall be incorporated into the operating and maintenance instructions.

Mechanical Testing

The Gravity Belt Thickener shall be tested under the full range of sludge loading conditions to determine satisfactory operation of the following:

(a) Correct belt tracking.

(b) Adequate sludge / polyelectrolyte mixing.

(c) Efficient mixing and flocculation in the mixing chamber.

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(d) Even distribution of sludge across the belt width.

(e) Efficient ploughing of the sludge on the belt to attain maximum dewatering.

(f) Efficient removal of the sludge from the belt by the scraper.

(g) Effective spray washing of the belt.

(h) Effective collection of wash water.

(i) Effective collection of filtrate.

(j) Continuous and effective lubrication of all bearings.

(k) Minimal production of aerosols from the belt cleaning action.

All pumps shall be tested in accordance with the relevant standard or particular specifications.

Performance Testing

The Gravity Belt Thickeners shall be tested under maximum sludge loading conditions to determine the following:

(a) Polyelectrolyte consumption.

(b) Thickened sludge dry solids concentration.

(c) Dry solids concentration in the filtrate.

From these tests, the following shall be calculated.

(a) The polyelectrolyte consumption per mass of sludge treated (Kg/tonne dry solids)

(b) The percentage of dry solids capture.

Control Systems Testing

The control systems as listed shall all be thoroughly tested for conformance with the specification by the simulation of tank liquid levels and malfunctions etc.

M23.11 QUALITY MANAGEMENT

Quality management criticality categorization: Major.

M23.12 MEASUREMENT AND PAYMENT

M23.12.1 General

Measurement and payment will distinguish between supply/delivery and installation/commission for each item of equipment as listed and priced only in the Schedule of Quantities. Payment will not be made for part supply of any listed item.

The respective tender item rates shall be deemed to cover all costs of equipment required within the scope of this Contract.

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The tendered rates or sums shall cover the cost of design, drawings, manufacture, supply, testing at the manufacturers works, delivery to site, off loading, installation, site testing, setting into operation, the supply of O & M manuals, commissioning and maintenance during the warranty period of all equipment specified and also for anything not specifically mentioned but obviously required, (e.g. all ancillaries, including all bolts, fastenings and brackets, safety guards and any work or material required for the proper installation of such equipment) to enable the equipment to be installed and/or function safely and correctly as specified. No claims whatsoever for extras will be allowed on the grounds that a necessary piece of equipment or a part thereof is not specifically mentioned.

M23.12.2 Testing

The tendered sum shall cover the cost of all plant and personnel for conducting the testing, and in the case of the workshop and preliminary testing shall include the cost of any consumables. For the acceptance testing, the consumables will be provided for the initial test only, by the Employer.

particular specification m23: gravity belt thickeners

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