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The Proven Grit Removal & Dewatering System

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WEMCO® Hydrogritter®

The Proven Grit Removal & Dewatering SystemThe WEMCO® Hydrogritter® has three major components: a pump, a cyclone separator/concentrator, and a dewatering/washing classifier. The pump pulls grit from the grit chamber or other source and feeds it to the cyclone separator. The grit is then captured/concentrated and discharged into the spiral classifier where it is washed and dewatered. The system automatically generates a low moisture grit suitable for final disposal.

WEMCO Model C or CE grit pump

Dewatered grit

Influent from grit chamber

Cyclone overflow (~235 gpm) Completely degritted for return to grit chamber, primary clarifier or thickner

How it works - mass balance

Cyclone feed (~250 gpm)1/8 inch x 200 mesh grit

Cyclone underflow (~15 gpm) contains virtually all the grit (95% of 200 mesh) plus the same percentage of organics present in the grit chamber

Classifier overflow (~13gpm) - organics and super fine grit

Pump feeds (~220 gpm) of grit (1/8 inch x 200 mesh) slurry to the cyclone

Grit discharge (~2 gpm)

Step 1 - Assume the grit chamber (or primary clarifier underflow in certain circumstances) is able to capture grit from 1/8” to super fine 200 mesh. A rugged, abra-sion-resistant WEMCO® Model C or CE Torque-Flow® pump pulls this grit from the grit chamber as a slurry and feeds it into the cyclone separator at a pressure of 8 psi. In this example, the flow rate is 250 gpm, which allows grit withdraw rates of over 1 1/2 tons per hour from the grit chamber at only a 1% concentration.

Step 2 - The cyclone takes the 250 gpm from the pump and captures virtually all the grit it contains. It then concentrates this grit into the underflow at the bottom of the cyclone (the apex), yielding a flow rate of 15 gpm. The balance of the flow, 235 gpm, is complete-ly degritted and exits the top of the cyclone through the vortex finder. From there it can flow by gravity to further treatment.

Step 3- The 15 gpm grit concentrate from the cyclone underflow dis-charges to a specially designed spiral classifier where the grit is allowed to settle. The settled grit travels up the spiral conveyor where it is dewatered and then discharged as a low moisture product ready for final disposal. In this example, the final product volume is ~2 gpm. The 13 gpm balance, containing light organics and grit finer than 150 mesh, flows over the weir at the end of the classifier where it can be piped to further treatment.

Hydrogritter Selection

Degritting is the process of concentrating, capturing and dewatering to a transportable level a very, very small amount of “grit” in a very large plant flow. Consider for example that even in old, combined sewer systems the grit loading rarely exceeds 5 cubic feet per mgd, which calculates to eight parts of grit in 10,000 parts of liquid.

Although the selection of the Hydrogritter components - the cyclone and classifier - is theoretically limited by the amount of solids each component can process, in reality, because of the very dilute nature of the grit concentration, the solids handling capacity of the components is virtually never an issue and the equipment is sized on parameters other than solids loadings.

Cyclone Sizing

The critical sizing issue with the cyclone as covered above is not gross solids removal capability and not even the cyclone itself, but rather the size of the suction and discharge piping from the grit chamber of primary clarifier feeding the cyclone. Consider:

The piping has to be large enough not to plug with tramp solids, so the minimum acceptable pipe size is 3”, with 4” being a more common selection.

The pumping rate through the pipe has to be sufficiently high to convey the grit from the grit chamber, or primary clarifier, through the entire piping system, including the vertical runs, without allowing deposition or sedimentation in the pipe.

Recommendations on minimum velocities vary widely, with many municipal reference texts saying 3 to 6 ft/sec, countered by slurry-pumping guidelines for mining slurries at 8 ft/sec to 12 ft/sec for a “normal” mix of grit ranging from 4 to 150 mesh. Field application experience shows success at ~6 ft/sec minimum for “normal” municipal grit, with a preferred velocity of 8 ft/sec.

That requirement dictates that the flow/pumping rate to achieve an acceptable velocity through the 4” pipe size, for example, be a minimum of 250 gpm for a carrying velocity of 6.5 ft/sec.

Therefore, the size of the cyclone and its selection is based on these minimum flow requirements, and with that feed, essentially “degrits/concentrates” all of the grit contained in the feed from the grit chamber and discharges it out the bottom (apex) as a ~10 to 15% grit slurry ‘underflow.’ Cyclone selection is shown below in Chart 1.

Classifier Selection

The underflow from the cyclone then is fed to the classifier, where the grit is allowed to settle and be removed by the spiral auger, with the liquid containing most of the organic and finer grit being discharged over the weir in the back of the machine. Similar to the cyclone selection discussion above, the critical sizing criteria for the classifier is not the solid loading, but rather the hydraulic loadings. Classifier selection is shown below in Chart 2.

The feed rate (cyclone underflow) determines the sizing and capture capability of the machine. Once the feed rate is specified from the cyclone underflow (Chart 1), select a classifier from Chart 2 below that will allow the capture of the desired mesh grit (65, 100 or 150 mesh).

The screw diameter and rpm determine the grit removal rate, which is shown in tons/hr., and total grit loading in tons/hr. can be calculated using a conservative grit weight of 90 lbs. per cu. ft. x total grit cu. ft. /24 hrs. x 2000 lbs./ton. Note: To allow proper grit settling/capture in the classifier pool and move the captured grit up the classifier ramp require peripheral screw speeds of not more than 35 ft/min. That in turn require the use of relatively large diameter screws at slow speeds, so the grit removal capability of these large screws will virtually always handle the normal grit loadings.

Chart I - Cyclone Selection

Inlet Pressure PSI (ft)

Model 1000C Model 1500C Model 2000C

Inlet GPM

U’flow GPM

Inlet GPM

U’flow GPM

Inlet GPM

U’flow GPM

7.5 (18) 250 15 500 32 750 6010 (23.1) 305 16 600 28 960 5015 (34.6) 375 18 730 28 1280 5020 (46.2 435 20 840 28 1570 60

Vortex Finder 4 6 7.5

Apex 2 3 4.5

Inlet/Overflow 4x6 6x8 8X10

Specific applications may require different apex/vortex finder combinations. Consult factory for details.

Chart 2 -Classifier Selection

Classifier Size & Tank Type

HP

Cyclone Underflow GPM Maximum Raking

Minimum Pool Area Sq. Feet

WeirLength

Feet

65 Mesh

100 Mesh

150 Mesh

GPM GPM GPM RPM TPH

12” S F

1/2 25 49

17 32

15 24 12 3/4

6 8.3

1.1 2.0

18” S F

1 57 107

37 70

28 52 8 2 13.8

19.91.7 3.2

24” S F

2 103 190

67 125

60 94 6 4 24.9

362.3 4.4

30” S F

3 160 310

104 202

81 140 4 5 37

542.8 5.6

Refer selection of larger unit to the factory.

Up to 1 1/2” thickness at wear points

Replaceable Ni-Hard wear plate

Slurry seal, no flush water required

100,000 hour minimum bearing life

WEMCO® Hydrogritter® - Construction DetailsA system designed to optimize each piece of equipment mechanically and hydraulically. The result is a consistent, automatic, long-term grit removal solution. The system of the hydrogritter, cyclone, and pump is a high performance grit removal solution providing low operating and maintenance costs.

Mining Proven Spiral

Features a large, heavy-duty pipe shaft for maximum robustness. Welded flights with replaceable wear shoes which are up to 3/4” Ni-Hard in 24” and larger sizes.

Apex (underflow)

Extra thick two-piece case

Vortex Finder Overflow

Lower bearing

Exclusive WEMCO grit-proof, oil-filled bearing requires no external lubrication, only annual inspection.

Hand wheel lifting device to raise spiral/bearing for easy inspection

Motor

Cyclodrive® Speed Reducer

Designed for shock loads of 500%. No documented overload failures in over 1000 installations.

V-belt drive

WEMCO® Model C severe duty Grit Pump The industry standard for nearly 60 years!

Fully recessed cup-type impeller

Thick rubber abrasion-resistant liner

High-efficiency inlet design

Grit

This pile of grit shows what the Hydrogritter can do.

WEMCO® Hydrogritter® Components

The Hydrogritter components are designed as a system to optimize each piece of equipment - both mechanically and hydraulically - to consistently produce long-term, high performance grit removal automatically with unmatched reliability and low operating and maintenance costs!

WEMCO Model C or CE Torque-Flow Pump - The industry standard for nearly 60 years.

The grit pump’s job is to pump the abrasive, destructive grit slurry to the cyclone without clogging or wearing out. The WEMCO Model C severe duty pump for continuous duty or the Model CE heavy duty are superably designed to do so, and features:

• A recessed impeller that pumps pipe-size solids - truly clog free performance.• 650 Brinell Ni-Hard or High Chrome material with 1” thick wear sections.• Cup-type impeller that actually improves the pump’s hydraulic performance as wear

occurs.• Robust mechanical design for years and years of trouble/maintenance-free performance.

WEMCO Cyclone - Efficient grit separation & concentration

The cyclone’s job is to both concentrate the grit and reduce the volume of liquid so that a smaller and more economical/efficient classifier can be used. The slurry from the pump is converted to rotational motion as it enters the cyclone inlet head. The resulting centrifugal force acts on the grit particles, driving them to the cyclone wall where they migrate down the decreasing diameter sections of the unit, eventually discharging through the cyclone apex. The degritted effluent exits the top of the cyclone through an opening called the vor-tex finder and is returned to the plant. Since the cyclone must also handle concentrated grit, its design, just like the Model C pump, is built to handle it:

• The interior of the cyclone is completely lined with heavy-sectioned natural or neoprene rubber for maximum abrasion resistance - just like they are for mining applications.

• The efficient in-volute inlet head requires only low pressure feed from the pump because it minimizes turbulence and short circulat-ing. Cyclone pressure is directly related to the pump’s speed, so low inlet pressure results in low pump speeds and less pump wear.

• A quick disconnect on the apex discharge assembly allows easy and rapid access for inspection or in case an oversized object needs to be cleared.

WEMCO Classifier - Optimum grit capture and dewatering. Built for decades of service.

The classifier’s job is to wash, dewater, and discharge the grit captured by the cyclone. Grit from the cy-clone’s apex is introduced into the pool area of the classifier at a specific point, selected so that grit courser that 150 mesh will settle but organics and finer grit will stay in suspension and be discharged over the weir. The spiral conveyor moves the grit from the pool area at the lower end of the machine up to the dis-charge point at the top, allowing it to dewater as it transverses the dry incline area. The dewatered product is discharged at a high enough elevation that most any receiving container can be used, making final disposal convenient. The classifier is also built - just as the Model C pump and cyclone are - to handle tough grit!

• Bullet-proof power train. The spiral is completely supported by bearings at the top and bottom ends.

- Exclusive grit-proof lower bearing requires only yearly inspection, no periodic maintenance required.

- Cyclodrive® roller reducer - provides unmatched reliability and overload/ shock tolerance. Again, no periodic maintenance, only yearly inspection.

• Heavy-walled spiral shaft, with protective wear shoes, up to 3/4” Ni-Hard in larger sizes.• No tank wear. Since the spiral is completely suspended between two bearings, it can operate with a bed of sand between the screw

and the tank, improving dewatering and eliminating tank wear common with shaft less conveyors. • No need for installed spares! Nearly 60 years of absolute reliable service has proven there is no need for the added cost of an installed

spare classifier.

• Process Benefits

Protect downstream equipment from grit damage

• No grit buildup in digesters.

• Downtime and grit removal costs eliminated.

• Eliminates premature failure of pumps, heat

exchangers, and piping.

Proven ability to remove fine (+150 mesh) grit

• All components engineered as a system to consistently remove unwanted grit.

• 200 mesh capture capability with special designs.

• Designs available from 1/2 to 200+ MGD.

• Complete system responsibility from WEMCO -

not just individual components.

Unit located for convenient grit disposal into truck, dumpster, etc.

• Since grit is pumped into the Hydrogritter, it can be placed at an elevation high enough to dump grit into truck, etc.

• Can be placed at any convenient plant location, allowing greater design flexibility.

• Equipment Benefits

Clean, reliable, automatic grit removal

• No exposure to grit by plant personnel.

• Grit only briefly exposed to atmosphere, so odor is minimized.

• Optional design available with airtight covers and provisions for vacuum exhaust.

• Needs no operator attention.

• Protects downstream equipment from wear and

abrasion.

All components are mining-proven for maxi-mum reliability to provide the most cost-effec-tive, trouble-free system available

• Components are “system engineered” for high ef-ficiency.

• 25+ year design life.

•Low capital cost.

• Model C or CE grit pump - true clog-free pumping, cup-type impeller, 650+ Brinell wear parts.

• Rubber-lined cyclone - maximum abrasion resis-tance.

• Spiral classifier - Cyclodrive speed reducer and grit-proof bearing require no maintenance, only annual inspection. No tank wear - spiral runs on bed of grit.

• So reliable that no installed spare is necessary.

WEMCO® Hydrogritter® - Typical Applications

Model C or CE Pump

Grit Cyclone

Classifier

Grit Disposal

Typical Installation

Vent to Atmosphere

Cyclone Overflow

Sloped Piping

Clean-out port for flushing grit line

Grit Chamber

Multiple Hydrogritter installation with optimal odor removal covers (piping by others)

Excellent Engineering Solutions

Weir Specialty Pumps

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