Chemical Metering And Process Control Strategies

Chemical Metering andProcess Control StrategiesTim Truax, Director of OperationsWade Trim Operations Services

Chemical Metering and Process Control Strategies Industrial Uses of Chemical DosingTypical EquipmentPrinciples of OperationProcess Control Strategies

Industrial Uses of Chemical Metering Water Treatment– Coagulation– Iron Sequestration– Disinfection Wastewater Treatment–––––Odor ControlEnhanced Primary ClarificationPhosphorous ControlSolids ConditioningDisinfection

Industrial Uses of Chemical Metering Boiler chemical feedClean-in-place (CIP) for food processorsAdding fruit slurries to ice cream, etc.Car washingGolf courses – fertilizers and weed killersGreenhouses – fertilizers and insecticidesHotels – pools and cooling towersPilot plantsPaint manufacturing

Typical Chemical Metering System Components Chemical Storage TankStrainerCalibration Column / CylinderMetering PumpPressure Relief ValveBackpressure/Anti-siphon ValveInjector

Chemical StorageTanks Inert (FRP orpolypropylene aretypical materials) Bulk tank/day tankcombinations arecommon for somechemicals Usually vented Electronic ormechanical methodof level sensing isnormal

Strainer Used where feedchemical is not pureor which can becomecontaminated ordegrade over time “Y” strainers are themost common Located between thechemical storage tankand calibrationcolumn

Calibration Column /Cylinder “Industrial-strength”graduated cylinders Not installed on allmetering systems Used to verify pumpoutput and to adjustoperating parameters Located “between” thestrainer and themetering pump

Calibration Column /Cylinder “Industrial-strength”graduated cylinders Not installed on allmetering systems Used to verify pumpoutput and to adjustoperating parameters Located “between” thestrainer and themetering pump

Metering PumpThe metering pump is a positive displacementchemical dosing device with the ability to varycapacity manually or automatically as processconditions require. It features a high level ofrepetitive accuracy and is capable of pumping awide range of chemicals including acids, bases,corrosive or viscous liquids and slurries.

Typical Metering Pump Application Conditions1. Low flow rates in mL/hr or GPH are required2. High system pressure exists3. High accuracy feed rate is required4. Dosing is controlled by computer,microprocessor, DCS, PLC, or flowproportioning5. Corrosive, hazardous, or high temperaturefluids are handled6. Viscous fluids or slurries need to be pumped7. The metered chemical is relatively expensive

Metering vs. Centrifugal Pumps: Flow vs. Pressure

Metering Pump Many different manufacturers Different Principles/Actions/Components––––Gear PumpDiaphragm PumpPiston PumpPeristaltic Pump Almost all metering pumps are of the positivedisplacement type

Metering Pump Many metering pumps demonstrate a pulsationdue to the action/mechanism involved Pumps with pulsation effects:––––Piston PumpsPeristaltic PumpsDiaphragm PumpsGear pumps (to a lesser degree) Pumps without (or minimal) pulsation:– Rotary lobe Pumps– Progressing Cavity Pumps

Discontinuous Flow: Pulsation Effect

Speed and Stroke Settings: Jolts of Chemical

Piston Pump Internal Componentshttp://www.miltonroy.com/Files/Milton Roy/Global/US-en/product files/Bulletin210-B 2005.pdf

Peristaltic Pump Internal Components

Diaphragm Pump Internal Componets Courtesy Milton Roy

Solenoid-actuated Diaphragm Metering PumpE Class metering pump. Property of WALCHEM, an Iwaki America Company

Degassing Valve Operation (e.g., hypochlorite)E Class metering pump. Property of WALCHEM, an Iwaki America Company

Pressure Relief Valve Prevents damage topiping and equipment ifa discharge valve isclosed Chemical relief port isalmost always plumbedback to the chemicalstorage tank These are locatedbefore thebackpressure/antisiphon valve

Backpressure/Antisiphon Valve Prevents siphoningwhen the dosing point islower than the pump Provides a consistentpressure against whichthe pump operates; thisimproves accuracy ofthe metering operation Typically installed justdownstream of thepressure relief valve

Pulsation Dampener Dampens the pressureand the flow from pumpsthat exhibit pulsing Internally, there is anelastomeric bladder ordiaphragm. Above the diaphragm,the space is filled withcompressed gas Below the diaphragm,the fluid being pumpedfills the chamber, furthercompressing the gas

In-line (static) mixer Another way to minimizethe pulsation effect Typically used inpolymer applications, butnot corrosive chemicalsituations, e.g., ferricchloride or alum Can significantly lowerchemical costs when themixture is more uniform(reduced dosages)

Pulsation Dampener This graph shows thesystem pressure withand without adampeners Note that the systempressure w/odampening is 800 psi,but that withdampening, thesystem pressure rises(915 psi and 980 psi)

Very Simple System Shows Inlet valveCalibration columnOverpressure returnMetering PumpPressure Relief ValveBackpressure/Antisiphon valveOutlet valve Doesn’t Include Chemical StorageTankPulsation Dampener

Skid-mounteddiaphragm pumps Isolation ball valvesbefore and after thebasket strainer Double-actiondiaphragm pumps Prominent pulsationdampeners

Chemical Metering and Process Control StrategiesPROCESS CONTROLSTRATEGIES

Process Control Strategies Document a technically-based operational strategy Similar to, but different from, a plant’s O&M manual Lists the equipment and tankage used to accomplish aspecific treatment objective, e.g., disinfection Instructional and reference guides for operators Useful for training new operators Addresses the interrelationship between two or moreprocesses

Elements of a Process Control Strategy SummaryProcess OverviewUnit Physical InformationTheory and Operational ParametersCommon ProblemsRelationship to Other Processes

Summary“Chlorine is added to the wastewater flow prior todischarge. With sufficient contact time and chlorineconcentration the number of pathogens in the wastewateris significantly reduced.”

Process Overview“Chlorination occurs after effluent filtration and prior todechlorination. Before the flow enters the chlorine contactbasin, a strong chlorine solution is added. The volume ofthe contact basin is large enough to ensure a chlorinationtime of at least 30 minutes even at high flow. During thisperiod pathogens in the water absorb chlorine and aredestroyed. Dechlorination, the removal of left overchlorine, occurs at the discharge of the chlorine contactbasin. The overall goal of chlorination is to maintaincoliform counts below the permit limits.”

Unit Physical Information Lists the number of pumps, tanks, etc. Identifies the capacity of each, in gpm, gallons,or whatever units are used Gives typical detention times for tanks with1. Design Average Flow2. Maximum Flows3. Current Flow rates Location and type of valves in/out of a process May reference manufacturer’s O&M manuals

Theory and Operational Parameters Describes the physical, biological and chemicalactions involved in the process Operating Parameters– Controllable example: dissolved oxygen– Uncontrollable example: wastewater temperature Monitoring Parameters and Targets Control Parameters

Monitoring Parameters What raw data will we use to evaluate the process?What are the expected values/ranges of the parameters?What are the target values?How often willwe monitor theprocess?

Control Parameters Things the operator can directly adjust or control Adjustments made based on monitoring parameters anddeviations from “target” values

Performance Parameters These are a subset of the monitoringparameters In some cases, the performance criteria aredictated by the NPDES or groundwater permit In other cases, the performance is related tocost, efficiency, or some other internallydetermined criteria

Common Problems section This section addresses the common problems that theoperators have observed The interrelationship of Control Parameters and CommonProblems needs to be addressed here– e.g., higher ferrous chloride feed rates may depressdissolved oxygen concentrations in the aeration tank “Typical” problems should be included, but not complex orinfrequently occurring problems– e.g., a filamentous bacteria problem would not beaddressed by a PCS. You would want an SOP!

Relationship to Other Processes This section discusses the flows into and out ofa process, and the effects of/to those otherprocesses Impacts to related processes during upset oroverload conditions should be discussed This section should guide the operator aboutwhich process takes precedence whenstrategies are in conflict, e.g., anaerobicdigester process control would override aprimary clarifier control strategy (usually)

Questions and(hopefully) Answersttruax@wadetrim.com

a process, and the effects of/to those other processes Impacts to related processes during upset or overload conditions should be discussed This section should guide the operator about which process takes precedence when strategies are in conflict, e.