10/13/12 Procedure for the design and sizing of an Inclined Plate Clarifier for the removal of settleable suspe…

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Procedure for the design and sizing of an Inclined Plate Clarifier

(parallel plate, lamella) for the removal of settleable suspended

solids

Table of Contents

1. Inclined Plate Clarifier (parallel plate, lamella) Theory of Operation

2. General Considerations

3. Inclined Plate Clarifier Decision - Flow DiagramDetermining if your process requires a clarifier or clarification system

4. Inclined Plate Clarifier Design - Flow DiagramBasic process in the design of an oil water separator or separation system

5. The Impact of Settling Rate on Inclined Plate Clarifier Design

6. Sizing the Clarifier or Clarification SystemInputting the accumulated data to the Hydro-Flo Clarifier Sizing Spreadsheet to accurately size a clarifier or clarification systemfor your application

7. Comparing and Evaluating Clarifiers and Clarification Systems from Different Suppliers

Reviewing and filling out the Hydro-Flo Technologies, "Application Questionnaire" will also help you gather pertinent information requiredfor the proper design and application of inclined plate clarifiers and clarification systems.

Inclined Plate Clarifier

(parallel plate, lamella) Theory of OperationBasic concepts and theories of clarification

If you are unfamiliar with basic inclined plate clarifier (plate settler, parallel plate clarifier, lamella plate settler, etc.) design principles, areview of the "Inclined Plate Clarifier (parallel plate, lamella) Theory of Operation" might prove helpful.

This basic document covers Stokes' law and other basic separation concepts.

General ConsiderationsInclined plate clarifiers are typically considered very simple devices. However, several factors that could potentially affect safety,efficiency, and proper management must be given careful consideration prior to the installation or modification of any clarifier orclarification system:

1. Flow RateIn general, clarifiers are sized by the flow rate verses the separation chambers "effective" surface area (or, as it is more commonlycalled. the "projected" surface area). Therefore, the effectiveness of any clarifier is affected by the flow rate. The slower the flow,the better the results.

2. Design CapacityA clarifier has upper limits to the amounts of suspended solids that can effectively accumulate while it is in operation. If too much"sludge" or settled suspended solids accumulate on the plates, it may carry over into the wastewater outlet chamber and end upbeing discharged to the environment. Proper clarifier design will take the plate spacing into consideration and also allow for theremoval and storage of accumulated sludge from the clarifier to ensure that the accumulated products do not effect the operationof the clarifier.

3. Maintenance PracticesThe ability of any clarifier to function properly depends upon the timely performance of required service and maintenance. Clarifiersmust be monitored and maintained by competent personnel who understand how the systems operate. Clarifiers should be giventhe same close attention shown to any other important piece of equipment. The operators, users, and maintainers of the clarifiermust be clear on who will be responsible for monitoring, inspecting, maintaining, and servicing the system. Frequent inspectionsshould be made of the system and all associated piping, valves, etc. to prevent operational and mechanical failures orinefficiencies. Sludge needs to be regularly removed from the clarifier to keep it operating properly. Additionally, leaks fromclarifiers can result in environmental pollution, which can trigger costly investigative studies and cleanups. Rigorousimplementation of a clarifier inspection and maintenance plan can prevent discharges from the clarifier that may contaminate theenvironment.

4. Suitability of Inclined Plate Clarifier System to ProcessA clarifier designed and installed to meet a past process requirement may no longer be suitable when process requirementschange and/or the original maintenance plan is no longer followed. A clarifier that is put to a use for which it was not originallydesigned may be damaged or may not function properly, and could become an environmental liability. For example, a clarifierdesigned to receive the wastewater discharge from a small heavy metal precipitation system will not be able to properly treatlarger wastewater volumes for removing chrome from a tannery effluent. Process changes can also result in changes to thephysical/chemical makeup of the wastewater being treated by a clarifier.

5. Contaminants Contained in the Wastewater StreamMetallic particles in the wastewater will settle into the sludge at the bottom of the clarifier. Solvents or fuel compounds may alsobe entrained in the clarifier's sludge. This sludge could require management under the Resource Conservation and Recovery Act(RCRA) as a hazardous waste, if it exhibits certain toxicity characteristics. Therefore, it is important to prohibit the discharge ofcertain types of potential contaminants into a clarifier, and to regularly analyze sludge samples to determine toxicity prior todisposal. General improvements in spill/drip control and containment of hazardous materials and solvents will also reduce theamount of contamination in clarifier discharges.

Inclined Plate Clarifier Decision - Flow DiagramDetermining if your process require a clarifier or clarification system

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10/13/12 Procedure for the design and sizing of an Inclined Plate Clarifier for the removal of settleable suspe…

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STEP 1:

Identify Wastewater SourceBuildings and areas, as well as ALL activities and processeswithin the buildings and areas, that generate wastewater

STEP 2:

Institute Pollution Prevention and Source

Elimination / Reduction ProceduresCan the processes that generate the wastewater be eliminated? Can the process be converted to a dry process?

STEP 2-A:

Process altered or eliminated, no further

discharge

STOPNo Further Action Required

STEP 3:

Source DiversionCan the process be moved to an area that has existingclarification equipment in place? Can the existing equipmenthandle the increased flow? Is moving the process, diverting theflow, economically feasible?

STEP 3-A:

Process relocated or discharge diverted

STOPNo Further Action Required

STEP 4:

Wastewater Compliance Evaluation

Identify permit limits on ALL pollutants generated at the site. Characterize raw wastewater prior to any treatment, ifappropriate. Characterize treated wastewater if existingtreatment equipment is in place.

STEP 5:

Discharge & Pretreatment Requirements

Does the raw wastewater meet permit limits and environmentalrequirements? Does the treated wastewater meet permit limitsand environmental requirements?

STEP 5-A:

Discharge meets requirements,

STOPNo Further Action Required

STEP 6:

New Clarifier or System Upgrades Required.

Proceed to Inclined Plate Clarifier Design - FlowDiagram

Inclined Plate Clarifier Design - Flow DiagramBasic process in the design of a clarifier or clarification system

10/13/12 Procedure for the design and sizing of an Inclined Plate Clarifier for the removal of settleable suspe…

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STEP 1:

Conduct a Wastewater Characterization StudyThe engineer / designer may conduct a wastewater characterization study to establish clarifier or clarification system designparameters.

The first step in a wastewater characterization study is to conduct the "Clarifier Settling Velocity" test. This bench test will helpdetermine the clarifier's "TARGET" effluent quality at a specific particle settling rate. If possible, you should conduct this test numeroustimes to allow for variances in your overall process.

STEP 2:

Determine the Type of Clarifier or Clarification System Necessary for Your ProcessEvaluate the results of the characterization study and determine the category of suspended solids to be removed. Decide what type ofclarifier or clarification system to use.

NOTE:Hydro-Flo ClariMax clarifiers are an excellent separation solution for complex, evolving processes. The Hydro-Flo ClariMax clarifiersare designed to evolve with your growing, expanding process requirements. These robust clarifiers can be retrofit with a variety of platepacks, increasing the efficiency of the separator as your process or discharge requirements change. Surface drag skimmers forprocesses, vapor tight lids, etc. are simple bolt on modifications.

STEP 3:

Do You Have an Existing Clarifier at Your FacilityIf there is an existing clarifier on site, evaluate if it may beupgraded to accept the total flow or partial flow from the proposedsource to reduce loadings.

STEP 3-A:

Will Upgrading the Existing Clarifier Bring the

Discharge into ComplianceCan the existing system be upgraded (by the installation ofalternate plate packs, etc.) or adding additional treatmentcapabilities, etc.

STEP 4:

Review Concerns and Requirements of the NewClarifier or Clarification System with the Engineer

/ DesignerList all provisions that need to be considered to ensure the newsystem will be accessible for maintenance, will meet site specificarea classifications (i.e.: seismic and explosion proof areaclassifications, etc.) and will meet all regulatory and effluentdischarge requirements.

STEP 3-B:

Can the Existing Clarifier be Used to Pre-treat theWastewater Prior to the New ClarifierEven if the existing clarifier is not capable of handling theproposed load, it may be useable as a form of pre-treatment orused in conjunction with the proposed upgrades.

STEP 5:

Write the Specifications for the New or Upgraded

Clarifier or Clarification SystemsWrite specifications for the new clarifier, the clarifier upgrade orthe new clarification system required to meet all the above listedconcerns and requirements.

STEP 3-C:Incorporate existing clarifier into design

STEP 3-D:If determined that the existing clarifier is nolonger suitable for its current use or isunusable in the new system, incorporate theclosure of the existing clarifier into thespecifications

STEP 3-E:Design the upgrade of the existing clarifier

10/13/12 Procedure for the design and sizing of an Inclined Plate Clarifier for the removal of settleable suspe…

4/5www.clarifier.hydroflotech.com/Engineering Data/Inclined Plate Clarifier design parameters.htm

The Impact of Settling Rate on Inclined Plate Clarifier DesignDetermining the hydraulic loading ratio required to meet your effluent requirements (ppm, mg/l) is an important step in the design andsizing of any clarification system. A small change in the hydraulic loading ratio can result in a large change in the size of the specifiedclarifier. For example look at the following spreadsheets.

Input

What isthe

ProcessFlow

Rate 100.00

What isthe

DesiredHydraulic

LoadingRatio 0.25

What isthe

DesiredPlate

Spacing 2.00

Output

RequiredPSA 400

Available Models

CrossSectionalVelocity

InFt/Min

TotalEffective

PSA

ActualHydraulicLoading

Ratio

139 - 10 - 1 - ST OR PB 1.02 559 0.18

139 - 10 - 2 - ST OR PB 1.02 559 0.18

129 - 8 - 1 - ST OR PB 0.87 512 0.20

129 - 8 - 2 - ST OR PB 1.02 439 0.23

127 - 6 - 1 - ST OR PB 0.68 479 0.21

139 - 6 - 2 - ST OR PB 0.61 532 0.19MODEL NOT

AVAILABLE 0 - 4 - 1 - ST OR PB #DIV/0! 0 #DIV/0!

120 - 4 - 2 - ST OR PB 0.51 399 0.25

Required Cubic Feet of Media Overall Plate Length Number of Influent Troughs

SludgeThickening

or PyramidHopper

EXAMPLE ONE

Input

What isthe

ProcessFlowRate 100.00

What isthe

DesiredHydraulic

LoadingRatio 0.40

What isthe

DesiredPlate

Spacing 2.00

Output

RequiredPSA 250

Available Models

CrossSectionalVelocity

InFt/Min

TotalEffective

PSA

ActualHydraulicLoading

Ratio

104 - 10 - 1 - ST OR PB 1.53 373 0.27

139 - 10 - 2 - ST OR PB 1.02 559 0.18

86 - 8 - 1 - ST OR PB 1.22 366 0.27

86 - 8 - 1 - ST OR PB 1.22 366 0.27

86 - 8 - 2 - ST OR PB 1.53 293 0.34

81 - 6 - 1 - ST OR PB 1.02 319 0.31

92 - 6 - 2 - ST OR PB 1.02 319 0.31

74 - 4 - 1 - ST OR PB 0.76 266 0.38

74 - 4 - 2 - ST OR PB 0.76 266 0.38

Required Cubic Feet of Media Overall Plate Length Number of Influent Troughs

SludgeThickening

or PyramidHopper

EXAMPLE TWO

The only change in the above spreadsheets was the "Hydraulic Loading Ratio". All other variables remain the same.

On the first spreadsheet the "Hydraulic Loading Ratio" was input at .25. On the second spreadsheet the "Hydraulic Loading Ratio" wasinput at .40. You will note that the model #'s (which represent the total cubic feet of media required) changed from a high of 139 cubicfeet to a low of 74 cubic feet. That is a 46% change in the total size of the separator.

Both examples are suitable for 100 gallons per minute. Both examples will remove the targeted suspended solid. The real worlddifference between all the listed clarifiers is overall clarifier efficiency.

This example should reinforce the importance of accurately conducting the "Test for Determination of Clarifier Hydraulic Loading Ratio"and the "Clarifier Settling Rate" studies. If you size a clarifier without knowing the target "Hydraulic Loading Ratio", you will have togreatly over size the clarifier, because erring on the safe side, you will have to size the clarifier for maximum efficiency.

Sizing the Clarifier or Clarification SystemInputting the Accumulated Data to the Hydro-Flo Clarifier Sizing Spreadsheet to Accurately Size a Clarifier orClarification System for Your Application

The final step is to insert the data into the "clarifier sizing spreadsheet".

NOTE:ALWAYS SPECIFY THE "SHORTEST" PLATE LENGTH FEASIBLE FOR YOUR INSTALLATION.

This is VERY important.

All things being equal (projected surface area and plate spacing), a clarifier with 4' long plates will generate better results than a clarifierwith 8' long plates.

A clarifier with 4' long plates (as opposed to a clarifier with 8' long plates) will accumulate 1/2 the amount of sludge on the surface of theplates. Lower accumulation of sludge per plate helps prevent sludge re-entrainment and clarifier fouling.

Also, shorter plates will lower cross sectional velocities and improve overall laminar flow conditions.

The trade off is that clarifiers with short plate lengths take up more floor space. A clarifier with 8' long plates will take up half the floorspace that a comparable clarifier with 4' long plates.

Comparing and Evaluating Clarifiers and Clarification Systems from

Different SuppliersIf you go to ten different clarifier manufacturers and ask them to size a clarifier for a specific application (even when giving them a writtenspecification), you will get ten different answers. Everyone bases the efficiency of their clarifier on their clarifier's projected surface area. But, other design variables are all over the map. Plate spacing will vary from 3/4" to 2", and more. The angles and configurations of theplates are vastly different from manufacturer to manufacturer. Overall clarifier volume, from the largest to the smallest designs, canfluctuate as much as 150%, or more.

When comparing one manufacturer to another, it is best to compare the volume of the separation chamber (or size of the plate pack) incubic feet verses the sell price. This ratio should give you the clarifiers cost per cubic foot of plate pack. This is important because thephysical size of the clarifier is the greatest factor in the cost, as well as the efficiency, of the device. The published projected surfacearea has a much smaller impact on the clarifier's overall cost and performance.

NOTE:DO NOT COMPARE CLARIFIERS BASED SOLELY ON THE AMOUNT OF PROJECTED SURFACE AREA!

This is VERY important.

Many clarifier manufacturers use the smallest plate spacing possible in their clarifiers. This allows them to post the largest projectedsurface area numbers possible, giving the customer the impression that they are purchasing the most efficient separator available.

Unfortunately, using the smallest possible plate spacing is not the answer. Care must be taken when specifying plate spacing. If theplate spacing is too narrow, the results will be excessively high cross sectional velocities and unacceptably high Reynolds numbers,improper plate pack distribution and short circuiting issues, as well as sludge re-entrainment and high volumes of floc carry over.

There are many clarifiers in the field built with 8 foot long plates and 3/4" plate spacing that are only capable of operating at30% of the designed flow rate! There are also many clarifier manufacturers who specify 1" plate spacing, but in fact, they areactually less than that because they do not account for the plate thickness in their calculations.

Make sure that, when you are talking about plate spacing, you are talking about the distance between the plates - not thedistance from plate center to center. On smaller applications, the difference does not amount to much, but on large projects,the difference can be substantial.

Also, many manufacturers claim that their clarifiers are 100% efficient. Current fluid dynamic studies have shown that even the bestdesigns are 85% efficient at best and that some are even as low as 50% efficient. We rate our clarifiers at a conservative 80%efficiency rating. Make sure that you receive confirmation of the clarifier's total projected surface area as well as the clarifier's"effective" surface area.

Hydro-Flo Technologies, Inc. - 3985 Commerce Drive - St Charles, IL 60174 - Phone 630-762-0380 - Fax 630-762-0390contact@hydroflotech.com

Copyright © 2002 Hydro-Flo Technologies, Inc.