DEWATERING CENTRIFUGES
PART 1 GENERAL
1.01 SCOPE OF WORK
A. Furnish all labor, materials, equipment and incidentals required and manufacture, assemble, shop test, deliver and install complete, one centrifuge for dewatering aerobically digested waste activated sludge.
B. The dewatering centrifuge manufacturer shall be responsible for providing as a complete package the centrifuge, shaftless screw conveyor, polymer system and digested sludge progressive cavity pump (centrifuge feed pump). The package system shall include, as a minimum, all controls and instrumentation specified herein and presented on the P&ID I-6 and
I-7. Additional associated networking hardware and other ancillary devices shall be included to establish the communication between the centrifuge PLC (Programmable Logic Controller) and the Plant PLC/SCADA Network.
C. The dewatering centrifuge shall be a complete unit and shall include but not be limited to:
1. A rotating assembly consisting of a bowl and scroll conveyor with main bearings, mounted on a frame.
2. An electric main motor drive assembly.
3. A scroll drive system consisting of an AC inverter duty motor or a DC variable speed back drive motor.
4. An external oil lubrication system for the rotating assembly's main bearings.
5. A centrifuge NEMA 4X local OIT panel to be installed locally in proximity of the
Centrifuge, which is located on the upper floor of the CSSD Building.
6. A centrifuge NEMA 12 control panel (complete with all motor starter/VFDs/controllers, PLC, OIT) to be installed in the Electrical Room, on the main floor of the CSSD Building.
7. Vibration isolators for the centrifuge and main motor.
8. A centrate chute.
9. A solids chute to a shaftless screw conveyor.
10. All flexible connections.
11. Polymer injection ring and mixing valve (shipped loose)
12. Auxiliary and accessory devices, equipment, or materials necessary for system operation,
or to interface equipment provided under this Section with equipment provided under other
Sections, shall be included whether specified or not.
13. Auxiliary and accessories devices, equipment or materials where not specified shall be as recommended by the manufacturer of the primary equipment. These devices, equipment, or materials shall be of the highest quality of their respective kinds.
C. Electric motors and power factor correction capacitors shall be furnished as part of the work of this Section.
D. Adjustable frequency drive systems furnished as part of the work of this Section. E. Facility Design
1. The DESIGN/BUILDER shall be aware that the Drawings are generic in their depiction of the centrifuge installation and that any adjustments in piping and support platform configuration may be necessary depending on the equipment selected.
1.02 RELATED WORK
A. Electric motors, are as specified herein,.
B. Pulse width modulated (PWM) variable frequency drives, are as specified herein.
C. Concrete work is included in Division 3.
D. Field painting is included in Section 09901.
E. Polymer Feed System is included in Section 11246.
F. Progressive Cavity Feed pumps are included in Section 11315.
G. Shaftless Screw Conveyor is included in Section 14501.
H. Instrumentation and control work, as specified herein. Instrumentation and controls provided in this section shall adhere to Instrumentation and Control Specifications in this Section.
I. Piping, valves, pipe hangers and supports and appurtenances, except as specified herein, are included in Division 15.
J. Electrical work, except as specified herein, is included in Division 16.
1.03 SUBMITTALS
A. Submit, in accordance with this Section, six copies of all materials required to establish compliance with this Section. Submittals shall include the following:
1. Submit shop drawings and complete performance data for the following items:
a. Rotating assembly with bowl and scroll conveyor.
b. Frame and casing.
c. Main motor drive assembly.
d. Scroll conveyor drive system.
e. Oil lubrication system for the rotating assembly's main bearings.
f. Centrifuge local OIT panel
g. Centrifuge control panel.
h. Vibration isolators.
i. Centrate chute.
j. Solids chute.
k. Flexible connections.
2. Submittals shall include:
a. Certified general arrangement drawing(s).
b. Certified foundation drawings showing anchor bolt locations.
c. Details of construction and dimensional data.
d. Total equipment weight and weight of single largest item or component.
e. List of manufacturer's spare parts for 5 years of operation, including packing, gasket, etc.
f. Minimum clearance distances around equipment required to access equipment for service/repair/removal.
g. Recommended petroleum oil lubricants (POL) products, by grade (winter and summer);
list two manufacturers with equal products; list product names and designation.
h. Quantity/quality requirements for electric power, water supply, air, drainage, HVAC, structural, etc, and any special requirements.
i. Complete master wiring diagrams, elementary diagrams and control schematics.
j. Descriptive literature, bulletins and/or catalogs of the equipment.
k. Data on the characteristics and performance of the units to indicate ability to meet the system performance specified herein, including current listing of all operating centrifuges of the size specified herein to define the manufacturer’s experience.
l. Complete wiring diagrams and suitable outline drawings showing such details as are necessary to locate conduit stubups and field wiring. Standard preprinted sheets or drawings simply marked to indicate applicability to this Contract will not be acceptable.
m. The weight and live loads created by individual pieces of equipment as well as the total weight of each centrifuge and ancillary equipment.
n. A complete bill of materials of all equipment. This includes a listing of all parts and materials provided under this contract including a description, manufacturer part numbers and quantity required for typical repairs.
o. Complete motor and drive, controls and instrumentation unit data.
p. Copies of all test results, as specified herein.
q. Descriptive literature on surface preparation and shop priming.
r. Complete data on noise as specified herein.
s. Bearing Life: Certified by the centrifuge manufacturer.
3. Electrical Shop Drawings and Diagrams. Furnish complete information on all electrical wiring and equipment, including:
a. Complete information on all electrical wiring and equipment.
b. Catalog information and performance specifications shall be provided on all devices such as, but not limited to, fused disconnects, motor starters, terminal blocks, AC or DC drive controllers, alarms, switches, lights, timers, relays and related equipment.
c. Connection diagrams showing the actual wiring within a complete electrical system or enclosure; with all wires and terminals numbered and identified.
d. Interconnection diagrams which shall show the actual wiring connecting all terminal points in complete systems with other complete systems and other isolated units or power sources; interconnections of all instruments shall be shown on Instrument Loop Diagrams in accordance with ISA Standards.
e. Panel and control station layouts giving the physical location of each item wired into the electrical system. These shall show the physical location within panels or cubicles of relays, meters, etc, and the location of any electrical component anywhere else in the system, so that the system may be maintained.
f. Schematic diagrams showing the wiring of each printed circuit board supplied, plus all external connections to the circuit board.
g. Provide logic diagrams showing the operation logic including process and safety interlocks. Instrument and logic diagrams and schematics shall be prepared using ISA Standard symbols with the identification letters as shown on the Process and Instrumentation Symbols and Legends.
h. Ladder diagrams shall show in detail all components of an entire system. Standard symbols shall be used wherever possible. Other symbols may be used, if approved by the Engineer, provided a legend identifying the meaning of each symbol is given. The numbers on the schematic diagram shall correspond to the numbers on the wiring diagram and other numbers on the actual wires. Where program timers or
cam-operated switches are used, sequence charts shall accompany the schematic.
i. A Sequence of Operation describing in detail the various steps of operation in their proper order.
B. Samples. Submit the following:
1. Sample of manufacturer's field observation/test data collection/recording form.
2. Sample of shop test data collection/recording form.
3. Sample of typical test report.
C. Design Data. Submit manufacturer's standard drawings, catalog cuts, technical data sheets and descriptive literature for the following items:
1. All items fabricated by the manufacturer.
2. All items purchased for use by the manufacturer.
3. Design Data. Submit for the following:
a. Main drive motor sizing.
b. Back drive/scroll motor sizing.
c. Main drive sheave and belt sizing.
d. Main bearings.
e. Back drive gearbox (D.C. Back drive), or scroll drive gearbox.
f. Back drive coupling.
g. Solids discharge chute and diverter.
h. Solids discharge chute diverter operator.
1. Submit proposed test procedures for the following:
a. Shop testing of the centrifuges.
b. Field testing of the centrifuges.
c. Laboratory testing of the tungsten carbide (TC) abrasion resistant material.
2. Submit the following test reports:
a. Shop testing of the centrifuges.
b. Field testing of the centrifuges.
c. Laboratory testing of the TC material.
3. If the equipment or material to be provided under this Section is not specifically required to be tested in compliance with the requirements specified, the manufacturer's standard test used for quality control of the equipment or material shall be submitted. The tests shall have been performed within 3 years of submittal of the reports for approval.
4. Test reports shall be accompanied by the certificates from the manufacturer certifying that the material and equipment propose to be supplied under this Section is of the same type, quality, manufacture and make as that tested.
E. Certifications
F. Manufacturer's Installation Instructions
1. Submit the manufacturer's instructions for delivery, unloading, storage, handling and installation of the centrifuge units.
G. Statement of Qualifications
H. Manufacturer's Field Report
1. Submit manufacturer's field report of inspections, tests and observations for all items furnished under this Section.
2. Include copies of original test data collection forms.
1. Complete operation and maintenance data shall be furnished for all equipment included under this Section, as specified in this Section. The maintenance instructions shall include maintenance plan for the equipment, troubleshooting data and full preventative maintenance schedules, recommended cleaning instructions, procedures and safety precautions for equipment and complete spare parts lists with ordering information.
J. Warranties
1. Submit warranties for work under this Section and special warranties listed below in compliance with this Section.
A. American Society for Testing and Materials (ASTM)
1. ASTM A36 - Standard Specification for Carbon Structural Steel.
2. ASTM A48 – Standard Specification for Gray Iron Castings.
3. ASTM A242 - Standard Specification for High-Strength Low Alloy Structural Steel.
4. ASTM A480 – Standard Specification for Flat-Rolled Stainless and Heat Resisting Steel
Plate, Sheet and Strip.
5. ASTM A500 - Standard Specification for Cold-Formed Welded and Seamless Carbon Steel
Structural Tubing in Rounds and Shapes
6. ASTM G65 - Standard Test Method for Measuring Abrasion Using the Dry Sand/Rubber
Wheel Apparatus.
B. American Concrete Institute (ACI)
C. American Institute of Steel Construction (AISC)
D. Instrument Society of America (ISA)
E. American Welding Society (AWS)
F. National Electrical Manufacturer’s Association (NEMA)
G. National Electrical Code (NEC)
H. Underwriters Laboratories Inc. (UL)
I. Institute of Electrical and Electronic Engineers (IEEE)
J. American National Standards Institute (ANSI)
1. ANSI B15 – Ball Bearings, Local Bearings and Fatigue Life
2. ANSI B16.1 - Standard for Cast Iron Pipe Flanges and Flanged Fittings Class 25, 125, 250 and 800.
K. American Gear Manufacturers Association (AGMA)
L. American Bearing Manufacturers Association (ABMA)
M. The Society for Protective Coatings (SSPC)
1. SSPC SP-6 – Joint Surface Preparation Specification Commercial Blast Cleaning
2. SSPC SP10 – Joint Surface Preparation Standard Near White Blast Cleaning
N. Where reference is made to one of the above standards, the revision in effect at the time of bid opening shall apply.
1.05 QUALITY ASSURANCE
A. Qualifications
1. Welders to be employed on the project shall provide evidence that they have passed AWS or DIN qualifications tests, within the previous 12 months. Submit evidence of compliance.
2. The centrifuge manufacturer shall have built similar equipment of similar type, size and capacity and must submit documentation demonstrating experience in design, manufacture and start-up of high solid dewatering centrifuges of similar capacity and complexity and provide documentation of at least three wastewater dewatering facilities each of which has been operating in the United States for 3 or more years.
B. Certifications
1. Certify that materials and equipment specified herein conform to the respective standards referenced.
2. Certify that shop test equipment has been calibrated.
3. Certify that field test equipment has been calibrated and checked.
1. A pre-installation conference will be held to confirm the scope of work and responsibilities of the attendees.
2. The conference will be held 4 weeks prior to commencing installation work.
3. The conference will be held at the plant site.
1. Provide services of a manufacturer's service engineer specifically trained on type of equipment specified. Submit qualifications of service engineer for approval. Work-day requirements listed below are exclusive of travel time and do not relieve DESIGN/BUILDER of obligation to provide sufficient service to place equipment in satisfactory operation.
a. Installation Assistance: As requested by DESIGN/BUILDER.
b. Start-up Assistance: Two 8-hour days to assist in check-out, start-up, calibration, functional testing, acceptance testing and performance testing.
c. Operations Training: Two 8-hour days of classroom and hands-on instruction which will cover the theory of operation, actual operation of the centrifuge, polymer systems (if furnished by the centrifuge manufacturer) and optimization of the centrifuge operations.
d. Maintenance Training: During the same time period as the above operations training, provide classroom and hands-on training in separate sessions for electrical
maintenance, instrumentation maintenance and mechanical maintenance. Each class or separate session shall be conducted in two sessions on consecutive days consisting of 4 hours each. This training shall be repeated one more time within the 2 year period following final acceptance of the equipment with 60 day notice from the Owner.
e. Post-Start-up Assistance: The equipment manufacturer shall schedule no less than five
8-hour days for visits to the site after initial start-up/acceptance to assure that operation of equipment is in accordance with manufacturer’s recommendations. No more than five visits shall be required. These visits shall be in addition to the visits required by the manufacturer to address warranty problems. These follow-up visits shall occur within 2 years of initial start-up/acceptance and shall be as required and called upon by the Owner to make these visits. Personnel making visits to the site should be fully familiar with the equipment and should be able to make recommendations for optimizing the system to achieve the most optimum dewatering conditions for the centrifuge facility.
f. Post-Start-up Maintenance Supervision: The equipment manufacturers shall schedule
no less than five 8-hour days to supervise maintenance of the equipment over the 2 year period following acceptance.
g. Allow the Owner to video tape all training sessions.
1.06 SYSTEM DESCRIPTION
A. General
1. Dewatering centrifuge(s) specified herein are of the "high cake solids type" intended to produce dewatered cake with higher solids content than that produced in conventional centrifuge units. Selection of this type of equipment was based on the ability of the high solids centrifuge to produce dewatered cakes of a nature that are economically handled in subsequent disposal operations. Failure to achieve the minimum cake solids specified and/or the consumption of polymers in excess of the maximum amount specified will result in significant financial impacts to the Owner.
2. Each centrifuge shall be continuously fed sludge conditioned with polymer by individual variable speed progressive cavity type sludge feed pumps. The sludge shall be fed into the center of the equipment where the solids are thrown against the wall of the bowl which is rotating at high speeds thus generating high centrifugal forces. The solids deposited against the bowl wall shall be continuously moved by an internal scroll conveyor to one
end of the machine where they are plowed up a beach and discharged out a solids discharge chute. The solids shall discharge into a screw conveyor. The clarified liquid shall continuously overflow adjustable weirs at the other end of the machine where it discharges into a centrate chute that is piped directly to the plant drain system. The centrifuges shall
be provided with scroll drives to infinitely vary the speed of the conveyor to optimize torque for sludge dewatering. Polymer will be continuously fed into the sludge by variable speed progressing cavity type polymer feed pumps.
B. System Responsibility
1. The centrifuge specified herein shall be furnished by a manufacturer who shall have sole responsibility for all the parts and components required for a complete and operable system.
C. Design Requirements
1. The centrifuge shall be capable of dewatering and thickening sludge having the following characteristics:
Dewatering
a. Type Sludge: Municipal
b. Sludge Composition (approx.): 100% Aerobically Digested, Waste Activated Sludge
c. Sludge Feed Concentration (percent VS): 2 to 4 percent
d. Average Sludge Volatile Content (percent VS): 40 to 60 percent
2. The centrifuges shall be manufactured to meet or exceed the following physical parameters: Dewatering
a. Minimum bowl diameter, (in) 20
b. Minimum total bowl length, (in) 150
c. Minimum sludge feed flange connection, (in) 2
d. Minimum polymer feed line connection, (in) 1/2
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e. Minimum centrifugal force
f. Maximum horsepower draw, all drives, backdrive
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3000g
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and auxiliary systems, not nameplate horsepower
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90 Hp
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g. Minimum Main Drive horsepower
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50 Hp
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h. Minimum Scroll Drive horsepower
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15 Hp
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3.
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The water supply available at each unit shall be as follows:
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a. Flow
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1) Lube Oil Cooling, (max. gpm) (protected water)
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15
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2) Bowl Flushing, (gpm) (process water)
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100
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3) Clean-in-Place Flushing, (gpm) (process water)
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20
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b. Pressure
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1)
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Lube Oil Cooling, (min psig)
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40
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2)
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Bowl Flushing, (psig)
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50
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3)
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Temperature, (degrees F)
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55 to 85
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4)
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Clean-in-Place Flushing, (psig)
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50
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D. Performance Requirements
1. When processing sludge with characteristics as specified above, each centrifuge shall be capable of the following:
a. Guaranteed Sludge Feed Rate (gpm)
exclusive of polymer: 150 gpm
b. Guaranteed Sludge Feed Rate
(lb/hr dry weight minimum)
exclusive of polymer: 2,000
c. Guaranteed Percent Cake Solids (percent min): 22
d. Guaranteed Percent Recovery
(suspended solids) (percent min): 95
e. Guaranteed Polymer Dosage (lbs. of active
polymer/dry ton feed solids, maximum): 20
f. Continuous processing rate including polymer flow (gpm) using sludge characteristics
as specified: 450
2. Polymer used to verify performance requirements shall be emulsion/dispersion type.
Alternate type polymers will not be acceptable.
1.07 DELIVERY, STORAGE AND HANDLING
A. Equipment and materials provided under this Section shall be delivered, stored and handled in compliance with this Section.
1.08 MAINTENANCE
A. Lubricants and Fluids
1. Furnish a one year's supply of lubricants and fluids for all equipment.
B. Spare Parts
1. One feed tube.
2. Two sets of main drive belts.
3. One set main drive bearings.
4. Two sets of scroll drive belts.
5. Two sets of scroll conveyor bearings and seals.
6. Two sets thrust bearings (if applicable per manufacturer’s design), seals and lockwashers.
7. One set feed port and solids discharge port liners/inserts.
8. Ten percent of the total number of tungsten carbide scroll tile assemblies provided on each centrifuge for each centrifuge.
9. One complete set of gaskets, O-rings, and seals.
10. Provide spare parts for the PLC provided. Spare parts shall meet all of the spare part requirements defined.
C. Furnish one set of special tools and accessories required for repair, adjustment and proper maintenance, including at least the following as applicable:
1. Pillow block bearing nut wrench (if applicable).
2. Plate dam removal wrench (if applicable).
3. Bearing puller (thrust bearing) (if applicable).
4. Pillow block bearing remover (hydraulic).
5. Seal holder
6. Wrenches and tools necessary for centrifuge disassembly.
7 Scroll extracting tool.
8. Bowl Maintenance Dolly.
1.09 WARRANTIES
A. Warranty
1. The centrifuge, including; main drive; back drive; gear box; lubrication system; instrumentation and control system; and appurtenances, furnished shall be warranted to be free from defects in materials and workmanship for a period of 2 years after successful completion of Acceptance Testing. The warranty shall cover all repairs including parts and labor for all systems and all costs for removal, transportation and reinstallation. Said warranty shall conform to the requirements herein and shall be in a form acceptable to and be for the benefit of the Owner and shall be submitted by the manufacturer. Replacement
of equipment caused by neglect or abusive operation shall be the responsibility of the Owner. If the equipment should fail during the warranty period due to a defective part(s), the part(s) shall be replaced in the equipment and the unit(s) restored to service at no expense to the Owner.
2. Back this warranty with a Warranty Bond equal to 50 percent of the centrifuge purchase price. The bond shall remain in effect for 2 years after the acceptance test is successfully completed.
1.10 DEFINITIONS
A. "Process water”, as used in this Section, is treated plant effluent.
1.11 SPECIAL COORDINATION
A. Coordinate design, fabrication and installation of the equipment to assure all utilities (sludge feed, process water, drains, polymer feeds, chutes, etc,) match with regard to size, location, method of support, etc. The unit shall be partially piped and wired from below and therefore there will be many floor penetrations for pipes and conduit. The size and location of these penetrations shall be coordinated with the manufacturer to position these penetrations as close to the connection point on the equipment as possible while allowing for ease of maintenance and the vibrating nature, i.e., need for flexible connections of the equipment.
B. This coordination effort shall take place during the shop drawing process and before the centrifuge foundations are poured. If additional penetrations are later found to be necessary, or penetrations provided during forming and pouring of the foundations are found to be of the wrong size or in the wrong location, provide new openings (core-boring) and patch the existing openings at no additional cost to the Owner
PART 2 PRODUCTS
2.01 MANUFACTURERS
A. Andritz – Model D5LL
B. Westfalia- Model CF-466
C. Centrisys – Model CS21-4
2.02 GENERAL
A. The centrifuge shall be a solid bowl, horizontal, scroll type unit and shall be specifically designed to handle the sludge specified above. The unit shall be capable of continuous (or intermittent operations) with minimum of maintenance.
B. Each unit shall be equipped with:
1. Vibration isolators.
2. Drive motor.
3. Belt guards.
4. Lubrication system.
5. Operating and starter controls.
6. Alternating current, direct current or hydraulic back drive.
7. Planetary gear reducer.
8. Vibration switch.
9. All other accessories as specified herein and required to operate.
C. Equipment furnished and installed under this Section shall be fabricated, assembled, erected and suitable for placement in proper operating condition in full conformity with the Drawings and this Section, engineering data, instructions and recommendations of the equipment
manufacturer. The centrifuge unit shall be the product of suppliers regularly engaged in the design and manufacture of centrifuges and shall be specifically designed for the intended conditions of service. Appurtenant equipment shall be new and shall be designed, fabricated and assembled in accordance with the best engineering and shop practices. Individual parts shall be manufactured to standard sizes and gauges. Components of the centrifuge shall be designed for the stresses which may occur during operation or for any additional stresses which may occur during fabrication, shipping, erection or maintenance. Individual parts shall be alike in workmanship, design and shall be interchangeable. Materials shall be suitable for service conditions and as described herein.
2.03 MATERIALS
A. Standard Materials
1. Unless otherwise specified, materials shall conform to the following:
a. Bowl Stainless steel, Type 329 or Duplex
b. Bowl wear strips Stainless steel, Type 316
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c.
d.
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Scroll
Scroll tips
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Stainless steel, Type 316, 317, 329 or Duplex
Sintered Tungsten Carbide; maximum loss of 3
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cubic millimeters when tested in accordance
with ASTM G65, Procedure A
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e.
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Feed tube
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Stainless steel, Type 316 or 317
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f.
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Base
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Fabricated carbon steel or cast steel with stainless steel cladding on all surfaces in contact with process material
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g.
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Upper case, if applicable
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Stainless steel, Type 316L
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h.
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Bottom case, if applicable
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Fabricated carbon steel or cast steel with stainless steel cladding on all surfaces in contact with process material or Type 316 stainless steel
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i.
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Main Bearings
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Grease or Oil lubricated, B-10 life of 100,000 hours or 100,000 hours calculated life at standard operating speeds in accordance to DIN ISO 281 requirements.
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j.
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Feed compartment
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Stainless steel, Type 316 or 317
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k.
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Feed compartment
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Field replaceable Adiprene or urethane liner or fused tungsten carbide spray or Flame Sprayed Coast 53C or equal
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l.
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Sludge feed nozzle/port
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Replaceable Adiprene, silicon carbide, or Sintered Tungsten Carbide liner; maximum loss of 3 cubic millimeters when tested in accordance with ASTM G65, Procedure A
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m. Case protection at solids discharge end Field replaceable Adiprene or urethane liner or stainless steel casing or equal.
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n.
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Solids chute
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Stainless steel, Type 316
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o.
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Centrate chute
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Stainless steel, Type 316
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p.
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Fasteners
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Stainless steel, Type 316 unless higher strength is recommended by the centrifuge manufacturer or specified herein
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q.
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Anchor bolts, nuts and washers
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Stainless steel, Type 316, sized as required by the centrifuge manufacturer
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B. The supplier of stainless steel castings and abrasion-resistant materials shall supply certified copies of the mill test results certifying that the materials supplied are in accordance with the applicable ASTM standards. Three copies shall be forwarded to the Engineer prior to the initiation of centrifuge fabrication. The mill test reports shall include:
1. The actual material analysis.
2. ASTM standard.
3. Date of manufacture.
4. Place of manufacture.
5. Manufacturer's name.
6. Markings on the materials to denote the batch number.
C. All abrasion resistant materials shall have a volume loss less than 3 cubic millimeters when tested in accordance with the ASTM G65, Procedure A, Standard Practice for Conducting Dry Sand/Rubber Wheeler Abrasion Tests. All test reports shall be furnished in English. Non-ASTM standards and requirements shall be referenced to appropriate ASTM.
D. Fasteners shall be all English or all metric, mixtures of both types will not be allowed. All wiring instructions shall be in English and electrical connections for others shall be in accordance with the NEC, NEMA and ANSI standards.
2.04 MATERIALS AND CONSTRUCTION
A. Bowl
1. The bowl shall be designed to operate at a minimum force of 3,000 x G at the inside bowl wall diameter and to withstand, with an adequate factor of safety, all centrifugal forces encountered during operation at design speeds. The bowl shall be supported on each end on cylindrical or spherical roller-type bearings, each of which shall be fitted for convenient external pressure oil lubrication.
2. The bowl shall be centrifugal cast of high tensile strength stainless steel. No exceptions will be allowed. All centrifugal cast material shall be examined for cracks, shrinkage, porosity, or other defects by means of a liquid penetrant test. Pool depth level must be readily adjustable via weir plates located at the large diameter end of the bowl where liquid is discharged. Solids shall be discharged from the small diameter (opposite) end of the bowl. Centrifuge designs with centrate return tubes are not acceptable.
B. Main Bearings
1. The main centrifuge bearings shall be ball or cylindrical roller-type bearings mounted in the housing or in split horizontal pillow blocks and shall be lubricated by a circulating oil system. Each pillow block shall be provided with a threaded female connection to permit the use of a lifting eye hook to facilitate inspection and maintenance of the main bearings. All bearings shall have a calculated B-10 life rating of not less than 100,000 hours or 100,000 hours calculated life at standard operating speeds in accordance to DIN ISO 128 requirements. Main bearings shall be equipped with 100 ohm platinum type RTD sensors to monitor bearing temperature, if return oil temperature is not monitored. Bearings shall be guaranteed against replacement within the first 15,000 hour period. Annual replacement of main bearings will not be acceptable.
C. Conveyor (Scroll)
1. The unit shall include a stainless steel horizontal cylindrical-conical scroll conveyor equipped with helical flights. The conveyor shall be independently mounted concentrically within the bowl. All scrolls shall be completely interchangeable. All conveyor bearings shall be anti-friction roller or roller type and sealed from process contamination, externally greaseable and easily accessible for proper maintenance or permanently grease lubricated. The bearings shall have a calculated B-10 life of not less than 100,000 hours or 100,000 hours calculated life at standard operating speeds in accordance to DIN ISO 128 requirements. Bearings shall be guaranteed against replacement within the first 15,000 hour period. Annual replacement of conveyor bearings will not acceptable.
2. The edge and the face of the flights on the conveyor shall be protected against abrasion from a minimum of 1 ½ wraps beyond the feed zone through the solids discharge end by a series of welded-on assemblies consisting of sintered tungsten carbide tiles. The remaining scroll conveyor edge and face shall be protected from abrasion by spray fused tungsten carbide particles. The bonding between wear surface and back-up tile shall be able to withstand a minimum shear stress of 5,000 lbs/sq in and a minimum edge wear of 1/2-in on the diameter must occur before the parent metal of the conveyor flight is exposed to wearing. Each tile shall be individually replaceable and shall have an ability to monitor wear by means of a visual inspection.
D. Case
1. The centrifuge shall be enclosed in a fabricated steel case with stainless steel cladding on
all surfaces in contact with process material. If removable upper case is provided it shall be of stainless steel or steel with stainless steel cladding in the centrate and sludge discharge compartments. A stainless steel case shall be provided with a brush finish. The solids end of the casing shall include a replaceable adiprene, urethane, or stainless steel liner. In order to limit splashing and air leakage, the casing shall be provided with Rulon; Espey or equal seals where the bowl hubs intersect the casing, a neoprene gasket on the machined flanges where the upper and lower casings join and a rubber Teflon lip seal or splash collector and drain on the feed tube.
2. The case shall also be designed to act as a protective guard and to provide a complete enclosure to minimize noise. The bottom of the case shall contain flanged centrate and sludge cake discharge connections. The case shall be provided with splash guards.
3. The case shall include flushing connection for cleaning the case. Provide a case drain to drain the case to the centrate chute or alternatively provide a case that drains by gravity to its respective centrate and solids discharge chutes, if required by the manufacturer’s design.
E. Feed Tube and Pipe
1. The feed connection to the centrifuge shall be a 2-inch minimum with 150 lb. flange.
2. Polymer flocculent addition to condition sludge feed shall be introduced through a minimum 1-in connection on the centrifuge feed pipe that bolts to the external end of the feed tube. In addition, a second point of polymer flocculent addition in the sludge feed piping, upstream of the centrifuge, will be provided to be used as necessary to optimize centrifuge performance and/or minimize polymer flocculent consumption.
3. Manufacturer shall supply polymer injection ring and mixing valve shipped loose from the centrifuge to be installed upstream of the centrifuge by the DESIGN/BUILDER.
F. Main Drive System
1. The centrifuge supplied shall be equipped with electric motors and V-belt drive system complete with necessary vibration isolators for the individual support of the motor and centrifuge. The belt drive system shall consist of multiple belts as required to provide full capacity and withstand the full starting torque of the system. Belt, pulley and gear box guards shall be provided for protection from all moving parts.
2. The unit shall be equipped with a main motor that operates on a 480 Volt, 3 Phase, 60 Hz power supply.
3. Drive motor shall be TEFC, severe duty, squirrel cage induction for operation on a Variable Frequency Drive, 1800 rpm, continuous duty, Class F insulation, 1.15 service factor, with a minimum guaranteed efficiency of 95.2 percent under full load and capable of making two complete starts in succession after coasting to rest between starts. In addition, the motor shall be capable of at least one restart within 1 hour after any shutdown. The motor shall comply with all provisions of this Section. The motor shall be provided with a NEMA 4X terminal box.
4. Motor bearings shall be grease lubricated, anti-friction type, minimum L-10 life of 40,000 hours, with two 3-wire, 100 ohm, platinum RTD temperature detectors embedded in each phase with leads brought out to terminal strips in a NEMA 4X terminal conduit box. In addition, provide 120 Volt, low watt density, silicone rubber type, anti-condensation motor space heaters with leads brought out to the accessory NEMA 4X conduit box.
5. Motor shall be of low noise design. Motor sound pressure level shall not exceed 85 dBA
measured at 3 feet under free field, no load conditions in accordance with IEEE Standard
85..
G. Gear Box
1. Either a hydrostatic motor, separate multi-stage planetary gearbox or cycle gearbox shall provide control of the differential speed between the bowl and conveyor. Either device shall be suitable for 24 hour per day continuous service. The gear box shall be designed with a safety factor and meet the requirements of AGMA. The gearbox shall be independently balanced from the centrifuge and interchangeable. Each gearbox shall be protected from damage due to high torque overload. A thermal overload protection device in the drive motor shall not be considered as providing for sufficient protection for the gear unit. If cyclo gearbox is used, it must be mounted outboard of centrifuge main bearing for ease of replacement.
H. Scroll Drive System
1. Scroll drive system shall be of the variable frequency drive (VFD) inverter type or direct current (DC) drive type to provide an infinitely adjustable differential speed variation over its full range of operation.
2. AC Variable Frequency Drive
a. A variable frequency drive (VFD) inverter shall be supplied to drive the scroll motor and control the differential speed between the bowl and scroll. The drive system shall be capable of a flying restart after any shutdown including a power outage.
b. The VFD shall produce an adjustable AC voltage/frequency output. It shall have an output voltage regulator to maintain correct Volt/Hz despite incoming voltage variations. The VFD shall be of the flux vector controlled, sine-coded, Pulse-Width Modulated type and comply with all provisions of this Section. Drive shall be constant torque type and factory tested for severe centrifuge duty. Scroll drive VFDs, in NEMA 12 enclosures; require remote mounting in dry, non-corrosive spaces.
c. The VFD scroll drive system shall operate on 480 Volt, 3 Phase, and 60 Hz power.
d. The scroll motor shall be TEFC, chemical duty, AC inverter duty, squirrel-cage induction for variable speed duty, maximum 1,800 rpm, continuous duty, Class F insulation with a B rise, NEMA A design, 1.15 service factor, with oversized cast iron terminal box. Provide motor with bimetallic motor over temperature high limit thermostat. Motor shall be capable of delivering full load torque across a 1,000:1 turndown. The motor shall comply with all provisions of this section.
e. Motor bearings shall be grease lubricated, anti-friction type, and minimum B-10 life rating of 40,000 hours of operation.
4. The scroll drive system shall be capable of operating in either a manual or automatic mode.
In the manual mode, it shall provide for operation at a specific adjustable scroll differential speed. In the automatic mode, it shall operate at a constant torque setting via an automatic torque module incorporated into the control panel PLC.
5. A control system for the scroll drive assembly shall be mounted on the centrifuge control panel described in Paragraph 2.10 below. The system shall control the scroll drive as described in the following two modes of operation. Automatic operation shall be possible in both modes.
a. Differential speed - maintains the preset differential speed between the scroll and bowl while the torque will vary within the preset limitations.
b. Constant torque - maintains constant torque by entering into the controller the desired torque control point and varies the speed within the preset differential speed limitations automatically in order to maintain the torque control point.
I. Lubrication System
1. Lubrication of main bearings shall be by means of an automatic grease system.
2.05 GUARDS
A. OSHA approved guards shall be provided for all gear boxes and belt drives.
1. The guards shall be minimum 11 gauge steel.
2. The guards shall completely enclose the entire drive system and shall be designed to minimize vibration and noise.
3. Guards, except for the main drive motor, shall have a hole with cover plate coinciding exactly with the shafts of all equipment to allow the rpm to be checked.
4. The guards shall be lined on the inside with minimum 1/2-in thick sound absorbing rubber foam where permitted by guard design for noise attenuation
5. Fasteners shall be externally accessible.
2.06 VIBRATION ISOLATION AND MONITORING
A. The centrifuge shall be mounted on rubber or spring type isolators. The number, capacity and vibrator constant of the isolators shall be as recommended by the isolator manufacturer for the load and impact resulting from operation of the centrifuge provided. Each spring type isolator shall be provided with built in leveling bolts and built in resilient shocks to control oscillation and withstand lateral forces in all directions. The isolators shall be self-leveling or designed for internal leveling and adjustment. Snubber inserts shall be oil resistant synthetic rubber. Housings shall be welded steel and springs shall be oil tempered high carbon chrome vanadium steel. After installation, the isolators shall be inspected and adjusted by a qualified representative of the isolator or centrifuge manufacturer. A maximum of 2.5 mils of displacement at operating speed will be acceptable under dry run shop test conditions.
B. A vibration monitoring system shall be furnished for each centrifuge. The system shall consist of a vibration sensing transducer mounted on the centrifuge with location to be determined by the manufacturer.
C. Movement between interconnecting structures, piping, discharge chutes, conduit, etc, shall be avoided. To ensure proper installation and to prohibit the propagation of vibration through connecting pipe, and equipment, provide flexible rubber hoses, flexible pipe connectors and other flexible connectors to the unit. Flexible connectors shall be provided for, but not limited to, the following items:
1. Flushwater Piping.
2. Flocculent Piping.
3. Cooling Water Piping.
4. Electrical Conduit.
5. Sludge Feed Piping.
6. Effluent/Centrate Piping.
7. Hydraulic Oil Lines.
8. Oil Lubrication Lines.
9. Case Drain.
10. Cake Discharge.
11. Centrate Discharge.
C. Flexible pipe connectors shall be by Red Valve Company, Inc.; Redflex Flexible Pipe; General Rubber; Garlock Flexomatic Pipe; or equal, and have physical and chemical characteristics suitable for the particular service. Flexible centrate and cake discharge connectors shall be between the centrifuge and the discharge chutes. Flexible discharge connectors shall be provided of black molded neoprene, two ply fabric reinforced with polyester cord and complete with stainless steel back-up flanges and hardware. Flexible discharge connectors shall have a minimum face-to-face flange distance of 6-in.
2.07 DISCHARGE CHUTES
A. A minimum 1/4-in thick Type 316 stainless steel centrate and solids discharge chutes shall be provided for each centrifuge unit. Each chute shall have dimensions, connections and general shape as indicated on the Drawings and as required by the centrifuge unit. Each chute shall be provided with a flange suitable for bolting to the flexible discharge connector. Hinged,
quick-opening inspection openings with gasketed watertight covers using De-Sta-Co type latches shall be provided on the side of each chute in accessible locations. Openings shall be reinforced to prevent leakage. The juncture of all joints in plates shall be continuously seal welded inside and out so that the chute is watertight. Stiffeners shall be provided as required to limit stresses and deformation in plates during shipping, installation and operation. The chutes shall be supported from the structures and not the centrifuge. All hardware shall be Type 316 stainless steel. Both chutes shall be provided with 1 1/2-inch sample connections with a quick disconnect cap and chain.
B. The solids chutes shall be lined with an adhesion resistant plastic to prevent the build-up of solids. The material shall be attached with Type 316 stainless steel countersunk fasteners after the material has been drilled to accept the fasteners.
C. Both centrate and solids chutes shall include an 8-in ANSI (vent) flange mounted as shown on the Drawings.
2.08 NOISE LEVEL
A. Each centrifuge shall be equipped with noise suppression devices such that the noise level at any point 3-ft from the centrifuge equipment and drive motor, while operating in a loaded condition, shall not exceed 89 dBA. Main drive motor shall be a low noise type.
2.09 SURFACE PREPARATION AND SHOP PAINTING
A. All exterior surfaces, except stainless steel, shall be prepared, primed and finish painted in the manufacturer’s shop as part of the work under this Section. Surface preparation and shop priming shall be as specified in this Section. Finish shop painting shall be a two coat epoxy, pheloic or polyamide paint system as specified in this Section. Paint schedule and colors shall be submitted to the Engineer for approval prior to painting.
2.10 FABRICATION
A. Shop Assembly
1. The centrifuges shall be assembled in the factory to check for proper fit, mating parts marked and then disassembled for shipment.
2.11 CONTROLS
A. All controls required for the operation, monitoring and control shall be supplied by the centrifuge manufacturer. Each centrifuge control panel shall have all control and monitoring functions as described herein and shown on the Piping and Instrumentation Diagrams.
B. Centrifuge shall be supplied with a free standing centrifuge control and VFD/starter panel that will be installed where shown on the Drawings. The panel shall not exceed 72-in wide, 24-in deep and 90-in high. In addition of the centrifuge free standing control panel, the centrifuge shall be provided with a separate local control panel with HMI interface to be located adjacent to the centrifuge. The local OIT control panel shall be provided in a 304 SS enclosure with a NEMA 4X rating.
C. The control and VFD/starter panel shall be accessible only from the front and made of brushed finish stainless steel, NEMA 12 cabinet and equipped with lifting eyes and suitable for top entry of conduit. Each control panel shall contain an emergency shutdown pushbutton, main power disconnect, main drive VFD, scroll drive motor starter, reversing magnetic combination motor starter with motor circuit protector and for an inclined screw conveyor, a main power disconnect with flange-mounted external operating handle, a programmable logic controller (PLC) with human machine interface (HMI), an alarm system, all controls to allow manual differential
speed control and automatic torque control, H-OA select switches, 30 mm start/stop pushbuttons and pilot lights for all centrifuge motors and valves, and temperature and vibration monitoring devices.
D. The control and VFD/starter panel shall contain all control devices, such as control power transformers, relays, switches, coils, fuses, time delays, contacts and terminal strips, etc. All indicating lights shall be light emitting diode (LED) type 8415 as manufactured by R. Stahl, Killark, or equal. Each panel shall contain a pad-lockable main control switch that switches control of the centrifuge to the centrifuge control panels. Provide control panel with a 15 Amp
120 VAC duplex service ground fault outlet and fluorescent service lamp with door activated switch.
1. Provide the following NEMA 12 rated devices on the front face of the panel as a minimum:
a. Main circuit breaker disconnect switch with flange-mounted external handle
b. PLC operator interface with multi-function keypad
c. Local/Remote Selector Switch
d. Red Alarm beacon
e. Test Lamp pushbutton
f. Alarm Acknowledge/horn silence pushbutton
g. Reset pushbutton
h. H-O-A Selector Switches for each motor
i. O-C-A Selector Switches for each valve
j. Red RUN pilot lights for each motor
k. Green OFF/READY pilot lights for each motor
l. Red OPEN pilot lights for each valve
m. Green CLOSED pilot light for each valve.
n. Emergency STOP pushbutton
o. Seven digit non-reset elapsed run hour meter
p. Audible alarm horn
q. Vibration monitor
2. In the automatic toque control mode, the scroll drive/backdrive shall be automatically adjusted to maintain constant torque, thereby compensating for varying feed characteristics while optimizing residence time and separation.
E. The systems shall include all necessary programmable controllers, microprocessors, electronics, sensors and related control system auxiliary apparatus furnished and installed under the direct supervision of the centrifuge manufacturer.
F. The centrifuge control system design shall enable startup and shutdown from centrifuge control panel, shutdown from the starter panel, and shutdown initiated from interlocks with equipment supplied by others. An emergency shutdown pushbutton shall be located on each starter and control panel.
G. The point of interface between the centrifuge control panel and other control systems shall be via a combination of dedicated terminal strips in the centrifuge panels and digital communications. The characteristics at these interface terminals shall be isolated 4-20 mA input and output modules for all analog signals and 24 VDC or 120 VAC for switching and digital signals. Terminal strips for analog signals shall be at least 12-in from terminal strips for power and switching functions. There shall be 20 percent wired spares on all types of inputs and outputs. . All wire shall be identified with number code. The panels shall meet all applicable requirements of NEMA and latest edition of the National Electrical Code and shall have the UL listing mark for industrial control panels. Panels shall be provided with nameplates and all face mounted devices shall be provided with nameplates and labels of laminated phenolic material with engraved letters legible up to 10 feet from the panels.
H. The centrifuge control system shall incorporate a "jog control" for each motor. The jog control shall be for the purpose of checking motor rotation, connections and maintenance purposes. A "Jog" switch for each motor shall be located at the centrifuge motor control centers for electrical maintenance purposes.
I. Power supply to the control system shall be 120 Volts, 60 Hz, derived from a control power transformer located in starter panel
J. Provide an uninterruptible power supply (UPS) in panel for PLC and all microprocessor-based electronic devices in the panel for providing minimum 10 minutes of backup time at full load. UPS shall be industrially rated continuous-duty, on-line, solid state, line interactive, single- phase uninterruptible power system.
K. Panel Wiring
1. All interconnecting wiring shall have 600-volt insulation and be rated for not less than 90 degrees Celsius.
2. Power distribution wiring on the line side of fuses shall be 12AWG minimum. Control wiring on the secondary side of fuses shall be 16 AWG minimum. Electronic analog circuits shall utilize 18 AWG shielded, twisted pair, cable insulated for not less than 600 volts.
3. Power and low voltage DC wiring systems shall be routed in separate wireways. Crossing of different system wires shall be at right angles. Different system wires routed parallel to each other shall be separated by at least 6-inches. Different wiring systems shall terminate on separate terminal blocks. Wiring troughs shall not be filled more than 60 percent visible fill. Provide separate wireways for both field and panel wiring.
4. All wiring shall terminate in a master terminal board, where each terminal is uniquely and sequentially numbered. Direct interlock wiring between equipment will not be allowed. The master terminal board shall have a minimum of 25 percent spares. Terminal blocks shall be arranged in vertical rows and separated into groups (power, AC control, DC signal). Terminal blocks shall be the compression type.
a. Discrete inputs and outputs (DI and DO) shall have two terminals per point with adjacent terminal assignments. All active and spare points shall be wired to terminal blocks.
b. Analog inputs/outputs (AI and AO) shall have three terminals per shielded pair connection with adjacent terminal assignment for each point. The third terminal is for shielded ground connection for cable pairs. Ground the shielded signal cable at the PLC cabinet only. All active and spare points shall be wired to terminal blocks.
c. Terminal blocks for analog circuits shall have test terminals and bypasses for testing and troubleshooting.
d. Wire and tube markers shall be the sleeve type with heat impressed letters and numbers.
e. Only one side of a terminal block row shall be used for internal wiring. The field wiring side of the terminal shall not be within 6-inches of the side panel or adjacent terminal or within 12-inches of the bottom of the panel.
f. Terminal blocks shall have labels indicating the terminal block numbers.
5. All wiring to hand switches, etc., which are live circuits independent of the panel’s normal circuit breaker protection shall be clearly identified as such.
6. All wiring shall be clearly tagged and color coded. All tag numbers and color coding shall correspond to the panel wiring diagrams and loop drawings prepared by the ISS. All power wiring, control wiring, grounding and DC wiring shall utilize different color insulation for each wiring system used. The color coding scheme shall be:
a. Incoming 120 VAC Hot – Black
b. 120 VAC Hot wiring downstream of downstream of panel circuit breaker – Red
c. 120 VAC neutral – White
d. Ground – Green e. DC wiring -Blue
f. Foreign voltage – Yellow
7. Provide surge protectors on all incoming power supply lines at each panel.
8. Each field instrument deriving 120 VAC input power from the control panel(s) shall have a separate power distribution circuit with circuit breaker or fuse with a blown fuse indication. Provide 24 VDC power supplies as required to power field instruments and panel devices.
9. Circuit power from the SCADA cabinet out to field devices (switches, etc.) that are used as discrete inputs to the PLAC input cards shall be isolated with an isolating switch terminal block with flip cover that is supplied with a dummy fuse. Isolation switch block shall be an Allen Bradley Model 1492-H7 or equal.
10. All PLC discrete outputs to the field shall be isolated with an isolating fuse switch terminal block with a flip cover and a neon blown fuse indicator. The single circuit fusible terminal block shall be an Allen Bradley 1492-H4 or equal.
11. PLC discrete outputs shall be supplied with a 5A interposing relay if needed.
12. No terminals shall be allowed to be mounted on the side of the panel.
13. The Allen Bradley Compactlogix PLC shall come equipped with several interfaces as follows: Ethernet interface to the plant’s SCADA network, interface to HMI on panel and local OIT panel and interface for programming the PLC.
14. All information and status from the centrifuge shall be provided to the plant’s SCADA system via the Ethernet network. The centrifuge PLC vendor shall supply a memory map of the PLC registers to the Engineer prior to testing. The vendor shall coordinate with the plant’s SCADA PLC programmer to ensure compatible configuration with the plant’s Ethernet network and SCADA system. Software communication shall be provided in contiguous registers. One set of registers shall be provided for writing discrete-type information, and one set shall be provided for reading discrete-type information. One set of registers shall be provided for writing floating-point information and one set shall be provided for reading floating-point information.
L. Control and status functions shall be displayed for centrifuge control panel by [CRT's display window] [HMI][OIT with a multifunction membrane-style keyboard entry system for indication of setup data, operating data, circuit analysis data and diagnostic parameters] and a combination of hardwired analog devices and control switches.
M. The control panels shall be equipped with an alarm system, including audible horn and rotating red beacon light, to protect the centrifuge from damage and attract the operator's attention. The system shall contain three pushbuttons for alarm acknowledgement, lamp testing, and resetting. The alarm acknowledge pushbutton shall silence the audible alarm and change the state of the beacon from flashing to steady. The reset pushbutton shall manually reset control circuits and de-energize the beacon. Provide first out alarm indication to simplify troubleshooting of multiple alarms.
1. The following alarm conditions shall initiate a signal to the Owner’s plantwide SCADA
system to stop the sludge feed pump and the polymer feed pumps:
a. High torque or hydraulic pressure.
b. High vibration.
c. Left/Right Bearing High Temperature
2. The following alarm conditions shall shut down the centrifuge, and initiate a signal to the Owner’s plan wide SCADA system to shut down the sludge feed pump and polymer feed pump:
a. High Vibration.
b. Lube Oil System Low Level
c. Lube Oil System High Temperature
d. Lube Pump Motor Overload.
e. Main Drive Motor Overload.
f. Main Drive Motor Bearing High Temperature
g. High Torque
h. Low Bowl Speed
i. Low Differential Speed
j. Left/Right Bearing Low Oil Flow
k. Left/Right Bearing High-High Temperature.
l. Drive Motor High Temperature.
m. Scroll Conveyor Motor High Temperature.
n. Scroll Conveyor Controller Malfunction
o. Low Oil Level On Hydraulic Scroll Drive
p. High Oil Pressure On Hydraulic Scroll Drive
q. High High Oil Pressure On Hydraulic Scroll Drive.
r. Emergency Shutdown Activity
s. Any others considered by manufacturer as essential to safe operation.
3. The following alarms from the Owner’s plant wide SCADA system will be displayed at the centrifuge control panel:
a. Sludge Feed Pump Fault
b. Polymer Feed Pump Fault
c. Inclined Screw Conveyor Fault
N. The alarm system shall function as follows:
Conditions Signal Beacon Audible
Normal Off Off Alarm Flashing-Bright On Acknowledge Pushed Steady-Bright Off Normal Again On Off Reset Pushed Off Off
O. The programmable controller shall be capable of the following:
1. Measure and Display (at a minimum):
a. Bowl speed.
b. Scroll conveyor drive gear shaft speed, if gear box is supplied.
c. Drive motor amperage.
d. Differential speed - scroll conveyor vs bowl.
e. Bearing temperature.
f. Scroll/backdrive torque (if applicable).
g. Vibration
2. Display and Modify (Control) Characteristics Constants/Setpoints (at a minimum):
a. Normal minimum differential speed.
b. Normal scroll/backdrive torque.
c. Maximum allowable differential speed.
d. Maximum scroll/backdrive torque
e. Minimum electrical resistance before departure from normal differential speed.
f. Maximum allowable electrical resistance to achieve max. allowable differential speed.
P. The following discrete and analog conditions, as a minimum, will be monitored by the Owner’s
plant wide SCADA system via the PLC’s serial interface port:
1. Centrifuge Starting/Stopping Status
2. All Alarms listed in Paragraph 2.10K
3. Local/Remote Switch in Local Status
4. Vibration
5. Torque
Q. Provide the following dry contact inputs, as a minimum, from the Owner’s plant wide SCADA
system as applicable:
1. Start/Stop Centrifuge Control
2. Start Permissive from Downstream Systems
3. Emergency Stop Signal
R. Provide the following dry contact outputs, as a minimum, to the Owner’s plant wide SCADA
system as applicable:
1. Run Permissive for Sludge and Polymer Feed Pumps
2. Centrifuge Started (Not ready for Sludge) Status
3. Centrifuge Running (Ready for Sludge) Status
4. Local/Remote Switch in Remote Status
S. Provide the following digital analog inputs, as a minimum, from the Owner’s plant wide
SCADA system as applicable via the PLC’s serial interface port:
1. Sludge Feed Flow in gpm
2. Polymer Feed Flow in gpm
T. The PLC shall control sequencing from startup to shutdown. All equipment, including the centrifuges, within the Dewatering Building will be monitored and controlled by a distributed control system located in the control room. The programmable controllers provided with the centrifuges shall be capable of providing a continuous output signal that provides the status of all centrifuge functions. The centrifuge manufacturer shall coordinate with the instrumentation system suppliers to assure compatibility between the systems. The centrifuge start-up and shut-down cycles should be able to be initiated from the central control system or the local centrifuge control panel
U. Normal shutdown of the centrifuge shall be initiated by a single push button “STOP” command from the local control panel or remotely from the Owner’s plant wide SCADA system. This "STOP" command shall instruct the centrifuge control system to begin its shut down sequence.
1. The “STOP” signal shall remove the sludge feed and polymer feed permissive and de- energize the main drive motor. The centrifuge control system shall maintain a preset differential speed to clear the remaining cake from the bowl during coast down. Upon reaching a select torque, the diverter/slide gate will close to the divert position followed by opening of the diverter/slide gate spray water valve. After sufficient time for removal of resident solids, the centrifuge control system shall open the bowl flushing water valve for cleaning. After a predetermined (adjustable) time period flushing and spray water flows shall cease. When this occurs, the scroll motor/backdrive system shall be stopped. The machine shall then coast to a standstill awaiting another operating cycle.
2. After an adjustable time period the "STOP" command has been initiated, the lube oil pump shall be stopped. The centrifuge shall not be allowed to start more than the stated number
of times per hour as recommended by the manufacturer of the motor. After a power failure, the lube oil pump shall restart automatically and complete its pump shut off cycle.
V. During normal operation an excessive solids build-up shall be detected by the centrifuge control system as a higher than normal torque or hydraulic pressure requirement. Should the torque or hydraulic pressure exceed a preset point, the "High" torque/pressure alarm shall energize. Should the centrifuge experience unbalanced load conditions where vibration exceeds a preset limit, the “High” vibration alarm shall energize. Both the “High” torque/pressure and/or “High” vibration alarms shall signal the Owner’s plant wide SCADA system to shut down the sludge feed and polymer systems. This action shall normally result in a reduction of torque/backdrive pressure and vibration as the build-up is removed from the bowl. These systems shall reset open when the torque/pressure and/or vibration falls to an acceptable limit operation and the sludge feed and polymer feed system interlock contacts shall close to allow the feed systems to restart. The high torque and high vibration conditions shall also automatically open the feed flushing valve. When the high torque alarm clears, the feed flushing valve shall close and the centrifuge resumes normal operation. The high torque or pressure control shall be not more than twice the normal operating torque or pressure. The controls shall also allow operation at a set differential speed with torque or pressure allowed to vary within the normal operating limits.
W. Emergency shutdown shall be initiated from the Owner’s plant wide SCADA system or by depressing the emergency stop mushroom type pushbutton on the control panel which will de- energize the centrifuge drive motor, scroll motor/backdrive and lube oil pump simultaneously and the bowl flushing water valve opened for an predetermined (adjustable) time period for cleaning. Depression of the emergency stop pushbutton shall signal the Owner’s plant wide SCADA system to shut down the sludge feed and polymer systems.
X. In the event that the above clearing action fails to remedy the high torque/hydraulic pressure condition and/or high vibration condition and the torque/hydraulic pressure and/or vibration continues to increase, the centrifuge control system shall respond by issuing a “High-High” torque/ pressure alarm at the centrifuge control panel in addition to issuing an automatic shutdown command as described above. This shall stop the main drive motor and remove the sludge and polymer feed permissive. The centrifuge shall be allowed to coast to a standstill.
1. The same procedure shall be followed for shutdown due to excessive vibration, lubrication oil problem, scroll motor/backdrive system problem, high bearing temperature or other malfunctions detected in the centrifuge system. Automatic shutdown due to faults shall require reset action at the centrifuge control system cabinet or the detection device before the unit can be started. The specific shutdown condition shall be displayed by the centrifuge control panel.
Y. During normal operation, if sludge feed is stopped and the torque or hydraulic pressure fall below a desired set point, the diverter/slide gate shall energize to the divert position. After the diverter/slide gate is closed, the solids chute flushing water valve shall open a sufficient time for removal of resident solids. The centrifuge shall continue to run until a normal shutdown command is given or a "restart" of the sludge feed is initiated.
Z. The entire centrifuge control system installation shall be installed strictly in accordance with instructions of and under direct supervision of a qualified representative of the centrifuge manufacturer. The start-up shall be performed by the centrifuge manufacturer’s representative.
AA. Two copies of any tapes, discs, other devices required to reload programmable controllers or microprocessors shall be delivered to the Owner after start-up is complete.
AB. Provide the interposing relays necessary for the PLC to receive non wetted, SCR type discrete output signals from the Owner’s plant wide SCADA system and to send dry, non wetted discrete input signals to the Owner’s plant wide SCADA system.
AC. Provide the equipment identification and warning nameplates on the control panel. Nameplates shall be adhesive backed, laminated plastic with minimum of 1-in white lettering on yellow backgrounds. The equipment identification shall be the panel’s equipment number and the warning nameplate shall read: “CAUTION! 120 VAC MAY BE PRESENT WHEN PANEL MAIN POWER CIRCUIT BREAKER IS IN THE OFF POSITION”.
PART 3 EXECUTION
3.01 PREPARATION
A. The manufacturer shall visit the job site at least 5 days before installation of the units to field verify the foundations and other conditions are complete and ready for installation of the units.
B. All equipment shall be properly labeled and crated to protect any and all components from damage during shipment.
C. All parts shall be properly protected so that no damage or deterioration will occur during a prolong delay from the time of shipping until installation is complete and the units and equipment are ready for operation.
D. Factory assembled parts and components shall not be dismantled for shipment unless permission is received in writing from the Engineer.
E. Finished iron or steel surfaces not painted shall be properly protected to prevent rust and corrosion.
F. After hydrostatic or other tests, all entrapped water shall be drained prior to shipment and proper care shall be taken to protect parts from the entrance of water during shipment, storage and handling.
G. No shipment shall be made until approved by the DESIGN/BILDER in writing.
H. A year's supply of the manufacturers' recommended oil, grease and hydraulic fluids required for the equipment operation shall be delivered with the centrifuges.
3.02 INSTALLATION
A. Installation shall be in strict accordance with the manufacturer’s instructions and recommendations in the locations shown on the Drawings.
B. Supply all "L" type anchor bolts with necessary nuts and washers for the mounting of all equipment supplied. The anchor bolts shall be minimum 3/4-in diameter and made of Type 316 stainless steel. Anchor bolt layout drawings shall be supplied to the Engineer with shop drawing submittals.
3.03 FIELD TESTING
A. Field Inspection
1. Factory representatives of the centrifuge manufacturer, who have complete knowledge and experience in the proper installation, startup and operation of the equipment, shall inspect the final installation and supervise the field acceptance tests of the equipment. No equipment shall be energized unless there is written authorization from the manufacturer or unless it is done in the presence of the manufacturer’s service representative. All controls, interlocks and alarms shall be checked in the presence of the Engineer to assure proper control and equipment protection.
B. Functional Test
1. Functional testing shall be conducted after the installation of the centrifuge and all appurtenances and the equipment has been operated for four hours without failure. At the beginning, middle, and at the end of this test, the operator will record all temperature indicators, pressure gauges, and flow indicators. All safety devices shall be checked for satisfactory operation. The no-load amperage of the main drive motor shall be recorded. The start timer and acceleration time to running speed shall be adjusted, if necessary. The belt tension shall be, checked and readjusted if necessary, at the end of the test. The complete unit shall be subject to field acceptance tests under actual operating conditions to determine that operation is satisfactory and in compliance with the requirements specified.
2. The functional tests shall be made under the direct supervision of the qualified representative of the centrifuge manufacturer and in the presence of the Engineer. Provide, calibrate and install all temporary gauges and meters, shall make necessary tapped holes in the pipes and install all temporary piping and wiring required for the field acceptance tests. Written test procedures shall be submitted by the equipment manufacturer to the Engineer for approval 30 days prior to testing.
3. The functional tests shall be initially made with water and without sludge to demonstrate that the equipment and appurtenances furnished under this Section:
a. Have not been damaged by transportation or installation.
b. Have been properly installed.
c. Have no mechanical defects.
d. Are in proper alignment.
e. Have been properly connected.
f. Are free of overheating of any parts.
g. Are free of objectionable vibration and noise as specified.
h. Are free of overloading of any parts.
4. The functional test shall also demonstrate satisfactory operation of all equipment, controls, interlocks and alarms. Any malfunctions that appear during the tests shall be corrected and additional testing performed, to assure that the problem has been corrected.
C. Acceptance Test
1. Prior to acceptance, the manufacturer’s representative shall operate the centrifuge for a 5 day 8 hour per day period under actual conditions with sludge from the wastewater facility to demonstrate that the installed equipment will operate continuously, trouble-free and meet or exceed the performance requirements. During this test, the manufacturer’s
representative shall record bearing temperature, lube oil temperatures, motor input, torque, speeds, differential speed, vibration and noise every hour and verify operations are within tolerances.
2. The manufacturer shall recommend a liquid emulsion polymer for testing. If requested by the centrifuge manufacturer, the Owner will supply the manufacturer with sufficient quantities of sludge to conduct bench-scale testing.
3. The Owner will furnish all operating and support personnel, power, water, chemicals and all other incidentals required to take samples and perform the tests specified herein. The Owner will be responsible for collecting all required samples and measurements.
4. The centrifuge will be fed sludge and polymer in a proportion recommended by the manufacturer’s representative.
D. Performance Test
1. After acceptance and prior to Contract Closeout, testing will be conducted to determine compliance with the performance criteria as specified in PART 2.
2. The unit shall be fed sludge and polymer and shall be operated until the unit reaches steady state optimum performance. The unit shall then begin a 3 day, 8 hour per day test period during which the average performance of the unit must equal or exceed the specified performance parameters. If the unit fails to equal or exceed that required, or cannot operate continuously for the three day period due to unit failure, that days’ test period shall be repeated. The centrifuge manufacturer will be given 30 calendar days to optimize performance to produce results to equal or exceed the specified performance criteria.
3. During each day’s performance test, the centrifuge manufacturer will be responsible for collecting all required samples and measurements at 1.0 hour intervals in order to make the following determination. The first set of samples and measurements shall be taken 1.5 hours after the beginning of the test run.
a. Sludge feed concentration – total suspended solids (% TSS)
b. Polymer feed – total solids (% TS)
c. Centrate concentration – total solids (% TS)
d. Centrate concentration – total suspended solids (% TSS)
e. Final cake discharged – total solids (% TS)
f. Plant water (one or two daily composites) total solids (% TS)
g. Centrifuge Feed (sludge + polymer + dilution water) – total solids (% TS)
h. Polymer feed rate in gallons per minute
i. Sludge flow rate in gallons per minute
j. Centrate flow rate in gallons per minute
k. Centrifuge discharge rate in pounds per hour
l. Solids capture in percent. Percent solids capture shall be defined as follows: Solids percent capture = (T/F) x (F-C)/(T-C) x 100
Where:
T = Cake Solids Concentration (% TS)
F = Sludge Feed Concentration (% TSS) C = Centrate Concentration (% TSS)
m. Setting for polymer feed pump
n. Setting for sludge feed pump
o. Differential speed (rpm)
p. Drive and backdrive torque
q. Motor amperage
r. Sludge feed – volatile suspended solids (% VSS)
4. The centrifuge manufacturer shall engage services of a certified independent laboratory acceptable to the Engineer to analyze the centrifuge manufacturer’s set of samples and make all solids determinations.
5. The centrifuge manufacturer shall prepare a formal test report including all laboratory analysis reports, measurements and calculations. Six copies of the certified report shall be submitted to the Engineer within fifteen days after completion of the tests.
END OF SECTION
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