SECTION 11320 GRIT REMOVAL PART 1 GENERAL 1.01 SCOPE OF WORK The grit removal system shall be complete with the following equipment: concrete chamber, grit storage hopper, drive unit, drive tube with impeller, grit removal pump, grit screw conveyor, electrical controls, and all other piping and appurtenances required or shown on the drawings. 1.02 RELATED SECTIONS Division 16 Electrical 1.03 REFERENCES National Association of Electrical Manufacturers Specifications. 1.04 DESCRIPTION A. The grit removal equipment will be installed inside the concrete influent channel of the headworks. The influent is tangentially introduced into the vortex chamber where impeller blades create a forced vortex causing the organics to separate from the grit and be lifted up with the effluent while the heavier grit particles settle to the bottom of the low chamber. A slurry pump pumps the grit into other dewatering equipment. B. Design Criteria Peak Flow Rate: Efficiency: Influent Channel Width: Effluent Overflow Width: Influent/Effluent Orientation: Upper Chamber Diameter: 7.5 MGD 95% of grit >50 mesh in size 85% of grit 50-70 mesh in size 65% of grit 70-100 mesh in size 30 inches 30 inches 360 degrees 10 ft Grit Removal 11320-1 S251-12-24
C. To maximize grit removal efficiency, the grit chamber hydraulics shall incorporate a toroidal flow path enhanced by a slow vortex. D. The grit moving across the bottom of the chamber shall be hydraulically scoured as the propeller blades rotate causing hydraulic currents to lift up the organics. The grit scouring intensity shall be adjustable. The grit shall pass from the removal chamber through an opening in the transition plate and drop into a grit storage hopper. E. The influent flume, transporting the liquid waste to the grit chamber, shall be of the size and shape shown on the contract drawings to assure that grit does not settle in the inlet flume and to provide for proper operation of the grit chamber. F. The grit removal pump can be either vacuum primed type or self-priming centrifugal type. 1.05 MANUFACTURER 1.06 SUBMITTALS The equipment specified in this section shall be Smith & Loveless Inc., Jones + Attwood, or WesTech. Substitutes, alternates, and or-equal manufacturers are not acceptable. A. Affidavit of Compliance Submit manufacturer's affidavit that all materials delivered comply with this specification and the cited standard specifications. B. Shop Drawings Submit shop drawings per the requirements of Section 01330. Show materials, size, detailed layout drawings drawn to-scale in Auto-CAD, with bill of material weight. Include details of required connections. Show interface and required spatial relationship between units and proximate structures. Provide wiring diagrams. Provide control panel details and layouts. Provide P&ID. C. Operations and Maintenance Data Submit bound copies of operations and maintenance data manuals per Section 01780. 1.07 DELIVERY, STORAGE, AND HANDLING Deliver in manufacturer s packaging and store per manufacturer s instructions. 1.08 SEQUENCING The responsibility of the Contractor. Grit Removal 11320-2 S251-12-24
1.09 WARRANTY A written supplier's warranty shall be provided for the equipment specified in this section. The warranty shall be for a minimum period of one (1) year from the date of Substantial Completion. Such warranty shall cover all defects or failures of materials or workmanship which occur as the result of normal operation and service. PART 2 PRODUCTS 2.01 EQUIPMENT COMPONENTS A. Grit Separator Drive Unit 1. The motor shall be TEFC, 3 phase, 60 Hz, 460 volt, minimum 1/2 HP, 1.15 service factor. The motor shall not be overloaded beyond the nameplate rating under any normal conditions encountered. 2. All bearings of the drive unit, including the motor, shall have a minimum L10 bearing life of 50,000 hours, except for the turntable bearing supporting the propeller assembly which shall have a minimum L10 life of 20 years. 3. The gearbox shall be specifically designed for this service. It shall have an opening for the torque tube driving the propeller. The gearbox shall be sealed and the bottom opening shall have an air bell around the torque tube to prevent water from entering the gearbox in case of flooding. The top of the gearbox shall have a bolted flanged connection for the grit discharge pipe. B. Drive Tube and Impeller Blades 1. The drive tube shall be solid stainless steel attached to the drive gear. The tube, pinions and gears shall be constructed of high quality steel, machined and hardened for high strength and long wear. 2. The impeller blades shall be fitted with the drive tube to rotate the upper chamber contents about the vertical axis. The impeller blades shall be constructed of Ni- Hard and shall have generously rounded leading edge to reduce energy consumption and prevent foreign material from fouling the propeller. C. Grit Storage Hopper 1. A concrete grit storage hopper shall have a 45-60 sloped bottom. To prevent squatty storage chambers the maximum diameter shall be 3-0. The minimum depth shall be 5'-5. This is to allow for adequate volume for grit pile expansion if backwashing is performed plus allow adequate storage to prevent excessive numbers of grit removal cycles and grit handling equipment wear. 2. The Manufacturer shall supply a 304 stainless steel cover plate over the hopper. The plate shall be provided in two sections to allow for removal and access to the lower hopper and shall include a circular opening centered over the hopper and sized to allow grit passage while minimizing organic capture. Grit Removal 11320-3 S251-12-24
D. Grit Removal Pump- Vacuum Primed Pump (by Smith & Loveless) 1. The Grit Pump shall be a 4" vertical, close-coupled, vacuum primed type with curved 5-vane flow inducer completely out of the flow path between the pump inlet and discharge connection, so that the grit pumped is not required to pass through the impeller. All internal clearances shall provide for the passage of a 4" spherical solid to preclude clogging of the pump and suction line. The pump shall be designed to be in-line mounted directly to a flange on top of the straight 4" suction line. The suction line shall be vertical, passing up through the grit chamber, drive, to prevent accumulated grit from flowing into the suction pipe during idle periods and clogging the suction line. The pump shall be vertical, for easy removal of the motor and impeller, to facilitate maintenance of the suction line by providing a straight path to any potential blockage. 2. The pump shall be of heavy cast iron construction, with Ni-Hard impeller, and especially designed for the use of mechanical seals and vacuum priming. 3. In order to minimize seal wear caused by lineal movement of the shaft, the shaft bearing nearest the pump impeller shall be locked in place so that end play is limited to the clearance within the bearing. The dimension from the lower bearing to the top of the impeller hub shall not exceed 6". 4. The bottom bearing of the motor shall be locked in place and designed to handle all thrust loads and the necessary radial load. The upper bearing shall be free to move up and down and thus carry only radial load. This movement allows for thermal expansion of the shaft. The shaft shall be solid stainless steel through the mechanical seal to eliminate corrosion and abrasive rust particles. 5. The impeller shall produce a turbine-like flow pattern within the casing, generating flow. To prevent grit from entering the seal area, all impellers less than full diameter shall be trimmed with the back shroud remaining full diameter so that a minimum clearance from shroud to casing is maintained. Both the end of the shaft and the bore of the impeller shall be tapered to permit easy removal of the impeller from the shaft. 6. The pump shall be specifically designed for vacuum priming. The pump shall have an adapter providing a large water reservoir above the impeller to provide for positive exclusion of air from the impeller. The seal shall be inside this area to assure lubrication and grit shall be excluded from this area by a full size impeller shroud. Pumps, which do not use hollow priming adapters for positive lubrication of the seal, will not be acceptable. 7. The pump shall be arranged so that the complete rotating element can easily be removed from the casing without disconnecting the electrical wiring or disassembling the motor, impeller, backhead or seal. 8. The pump shall be sealed against leakage by a single mechanical seal, constructed so as to be automatically drained and automatically primed each time the pump is drained and primed. Water which lubricates the mechanical seal shall be automatically drained from around the seal if the pump loses prime; in order to allow both the pump and the seal to be drained, thereby preventing freezing and breakage of the seal during power outages in sub-freezing temperatures. Grit Removal 11320-4 S251-12-24
9. The seal shall be of carbon and ceramic materials with the mating surface lapped to a flatness tolerance of one light band. The rotating ceramic shall be held in mating position with the stationary carbon by a stainless steel spring. 10. The grit pump shall be capable of delivering 250 gpm at 28 feet TDH. The maximum allowable speed shall be 1760 RPM. 11. The pump motor shall be TEFC, NEMA P-base, squirrel-cage induction type, 10 HP, 3 phase, 60 Hz, 460 volt electric current. It shall have a 1.15 service factor. The motor shall have normal starting torque and low starting current, as specified for NEMA Design B characteristics. 12. A bearing cap shall be provided to hold the bottom motor bearing in a fixed position. Bearing housings shall be provided with fittings for lubrication as well as purging old lubricant. The motor shall be fitted with heavy lifting eyes or lugs, each capable of supporting the entire weight of the pump and motor. 13. A vacuum priming system shall be furnished to prime the main pump. Vacuum pump shall have corrosion-resistant internal components. The vacuum priming system shall be complete with large port vacuum control solenoid valves, vapor filters to protect the solenoid valves, Sonic Start prime level sensor, floatoperated check valves to protect the vacuum pumps, and all necessary shut-off valves, including the pinch valve. The float-operated check valves shall have a transparent body for visual inspection. All hoses and tubing used in the priming system shall be at least 3/8 nominal diameter and provided by the Grit System Manufacturer. 14. The solenoid valves used in the vacuum priming system shall be of the high flow, direct acting ss body type, with threaded ports, NBR seals and 300 Series stainless steel plunger, rod, plate and springs. The minimum orifice diameter shall be 5/16. The solenoid valves shall be UL Listed, with Class F coil rating and of suitable voltage and thermal capacity for the application. 15. Each solenoid valve shall be protected by a vapor filter, installed in the vacuum line between the valve and the priming dome. The vapor filter shall be constructed of corrosion resistant materials and shall have a minimum filtration area of 2.74 square inches and be suitable for operation from 25 Hg to 100 PSI. They shall be readily replaceable without the use of special tools. 16. Liquid level in the pump priming chamber shall be monitored by a Sonic Start resonant frequency liquid level probe. The probe shall be equipped with a piezoelectric drive and sensitive circuits to detect frequency shifts when the probe is covered by liquid. The probe shall be completely sealed and have a 316L stainless steel housing for corrosion resistance. It shall be provided with a wiring connector molded of PolyPhenylSulfone, an amorphous high performance thermoplastic for impact and chemical resistance. The probe shall have a plug-in connector to facilitate easy removal. 17. The Sonic Start probe shall be provided with light emitting diodes. This diagnostic tool shall indicate connectivity, prime status or a fault condition. Systems utilizing an electrode, mechanical means such as a float, or that require any type of electrical or moving parts inside the priming chamber, which may Grit Removal 11320-5 S251-12-24
accumulate debris, short out, bind or fail will not be acceptable. 18. The priming system shall automatically provide positive lubrication of the mechanical seal each time a main pump is primed. To prevent excessive stoppage due to grease accumulation, no passageway in the priming system through which the pumped liquid must pass shall be smaller than the equivalent of a 2-1/2 opening. E. Grit Removal Pump- Self-priming Centrifugal Type (by WesTech) 1. Self-priming centrifugal pump shall be horizontal. The pump shall be furnished complete with a ductile iron volute capable of passing a 3 sphere solid, hard iron (ADI) with 400 BRN hardness impeller and seal plate, and wear plate of hardened alloy steel. Adjustment of the impeller face clearance (distance between impeller and wear plate) shall be accomplished by external means with no special tools or shims. The pump shaft shall be 4150 alloy steel with a double oil lubricated mechanical seal with silicon carbide faces, assembled on a replaceable 4130 alloy steel shaft sleeve. Suction and discharge spool flanged shall be one-piece cast iron, class 30. Each spool shall have one 1-1/4 NPT and one 1/4 NPT tapped hole with pipe plugs for mounting gauges and other equipment. The pump shall be mounted on a common base plate (pump over motor design) with the applicable configuration motor with constant speed V-belt drives and guard. 2. The pump motor shall be designed for non-overload operation conditions and should be suitable for service in wet conditions. The motor shall be a NEMA design, 1800-RPM, TEFC, severe-duty unit with 1.15 service factor. Power supply to the motor shall be 3 phase, 60 Hz with 230-460 VAC. F. Grit Concentrator 1. A 250 GPM second stage Grit Concentrator shall be provided as shown on the drawings for secondary treatment of organics and secondary grit dewatering. The Concentrator shall operate on the constant rate vortex principle. Design shall be such that a small volume of water and the grit will discharge at the bottom for final dewatering and ultimate disposal of the grit. 2. As a minimum, 90 percent of the water pumped to the Concentrator and 95 to 96 percent of the residual organic material shall flow out the top and be returned to the inlet channel to the Grit Chamber. The unit shall be capable of intermittent operation with minimal variation in removal efficiency. There shall be less than 5% putrescible material in the recovered grit from the underflow. 3. The Grit Concentrator shall be constructed of Ni-hard, with a minimum thickness of 1/2". Inlet and outlet connections shall be as shown on the drawings. The Grit Concentrator shall be provided by the Manufacturer of the Grit Chamber, for installation by the contractor. The operating range shall be compatible with the total grit removal system as described herein. G. Grit Screw Conveyor 1. The Grit Screw Conveyor shall be constructed with a 304 stainless steel inlet hopper to receive the mixture of water and grit. The hopper shall provide adequate Grit Removal 11320-6 S251-12-24
volume to ensure that the inflow grit and water mixture has sufficient retention time for full separation of the heavy grit from the water and residual light organic solids. An overflow weir shall be provided to return the water to the system. The conveyor shall be freestanding with 304 stainless steel support legs to hold the conveyor at an angle of approximately 22-25. The discharge shall be 8" diameter as minimum, plain-end 304 stainless steel pipe. The drive assembly shall be located at the discharge end. 2. The Grit Screw Conveyor shall have a minimum 3/16-in 304 stainless steel U-trough. The screw shall be a minimum 9-in diameter. The conveyor shall be 15-ft minimum horizontal length, with a minimum discharge height of 7-ft. 3. The inlet end shaft bushing shall be capable of being greased. The inlet end shall have at least one 2" drain. Clearance between the legs and the discharge outlet shall be as shown on the drawing. 4. The drive to the conveyor shall be a shaft mounted helical gear reducer. The motor shall be a minimum 1 HP, TEFC, 3-phase, 60 Hertz, 460 volt, with motor space heater. The screw speed shall be 9 RPM as minimum. The drive shall be mounted on a plate at the discharge end and the plate shall be bolted to the flanges on the trough. H. Electrical Control 1. The equipment supplier shall furnish all electrical items specifically called for in this section. The contractor shall supply all other electrical items, and interconnecting wiring of proper size, including all conduit and supports required to place the equipment into service. 2. Manufacturer shall supply one 480 volt primary control panel in a NEMA 4X type 304 stainless steel enclosure suitable for wall mounting with the following components to provide proper operation of the equipment: a. Main disconnect with through door interlock handle. b. Step down control transformer. c. Branch circuit protection. All 480V breakers shall be rated 65,000 AIC d. Vortex and pump drive motor starters. e. Emergency stop pushbutton. f. Vortex drive On-Off selector switch. g. Hand-Off-Auto selector switches for the pump and water scour. h. Cycle start pushbutton. i. Hour meter for each motor. j. Control power and run indicating lights. k. Alarm light indicating over current, and starter overload. l. Alarm reset pushbutton. m. Programmable control relay to provide necessary control logic and monitor equipment mounted electrical devices. Grit Removal 11320-7 S251-12-24
n. Run and alarm auxiliary contacts for use by the customer. o. Main Circuit Breaker p. UL 508A Label 3. Provide the following auxiliary contacts for Plant SCADA System remote monitoring 1. Grit Paddle Drive Running 2. Grid Paddle Drive Fault 3. Grit Pump Running 4. Grit Pump Fault 5. Grit Screw Conveyor Running 6. Grit Screw Conveyor Fault 7. E-Stop 8. Priming Fail 9. Conveyor Motion Fail 10. Auto Position PART 3 EXECUTION 3.01 INSTALLERS The Contractor 3.02 EXAMINATION Verify compliance with the specifications before installation. 3.03 FIELD SERIVCE The equipment supplier shall provide the service of a qualified representative for two trips (8 hours each) to inspect the equipment installation, assist in start-up, and instruct plant personnel in the proper operation and maintenance of the equipment. 3.04 MAITENANCE The contractor shall maintain the equipment installed under this section until the Notice of Substantial Completion and the beginning of the warranty period or the time that the owner begins using this equipment in the manner designated by this section for normal wastewater treatment operations. Grit Removal 11320-8 S251-12-24
3.05 FIELD QUALITY CONTROL A. Operational Test. Prior to acceptance by Owner, an operational test shall be conducted to determine if the installed equipment meets the purpose and intent of the specifications. Tests shall demonstrate that all equipment is acceptable; it is safe and in optimum working condition; and conforms to the required operating characteristics. B. Cleaning. Newly installed equipment shall be presented to the owner free of marks, dirt, grime, or the like. 3.06 DEMONSTRATION Contractor shall demonstrate the operability of the equipment to the owner and its engineer. END OF SECTION Grit Removal 11320-9 S251-12-24