h1. Nonlinear Chemical Dose Controller
h2. Abstract
The nonlinear chemical doser (CD) wasis designed to accommodatefor turbulent flowchemical indoes the chemical doser tubingflow rates. The previous chemicalCD doserdesign design,for thea [Linearlinear Chemical DoserCD| Chemical Doser], requires that the alumchemical flow beis laminar. This design uses the relationship between laminar flow and major losses in the doser tube to maintain a constant chemical dose with varying plant flow rates. However, when the flow in the dosing tube is turbulent, majorthe losseslinear canrelationship no longer create this linear relationshiplogner exists. In this case, a nonlinear CD, one that uses minor losses to control flow rates, is necessary to maintain a constant chemical dose with the varying plant flow rates.
The advantage to designing a nonlinear CD is that higher chemical flow rates can be used. This is necessary in In larger water treatment plants where larger chemical flow rates are necessary to dose alum and chlorine. The limit of the current flow control module is 400 ml/min. This maximum flow has been adequate for the plants currently in operation (La 34, Ojojona, Tamara, Marcala and Four communities) given their low flow rate capacityrates. As the demand for larger AguaClara plants grows, larger chemical dose flow rates will be required. Furthermore, headlossat high chemical flow rates, the head loss through the [flow control module orifice| Flow Controller] increases as chemical flow rate increases and as a result, requires requires that the chemical stock tank to be elevated to an unreasonable height.
h3. Methods
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h3h5. Methods
Figure 1: Nonlinear CD Design
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The non-linearnonlinear doser uses a dose control orifice (minor losses) instead of a dosing tube (major losses) to control the relationship between changing plant flow rates and chemical dose. The entrance to the rapid mix tank is also an orifice;. thereforeTherefore, theboth plant and chemical flowsflow varyrates inare directdominantly proportioncontrolled toby eachan otherorifice. The relationshipCD betweenuses chemicala doselever andarm turbidity will be changed manually as it is done with the linear CD.
To reduce head loss throughto increase head in the flow control module orifice,when athe newplant flow controllerrate isincrease. beingThe usedincrease in thehead design.drives Thethe modulechemical beingflow usedrate isto aincrease [PTwith 75 LS|http://floatvalve.com/pt75ls-detail.html] Kerick Valve. This valve was chosen to minimize flow control module size and maximize orifice area. The flow controller will housed in a square tub.
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h5. Flow Controller for Nonlinear module
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the plant flow rate. The relationship between chemical dose and turbidity is changed manually in the same fashion as the linear CD.
A lever arm similar to thelinear designCD forlever thearm linear CD will be used to relate plant flow rate to alum flow rate. A larger dosing tube is required to minimize major losses. This tube must be flexible to accomodateaccommodate lever arm motion. Flow will be channelledchanneled through the dose control orifice into a channel. This channel will deposit chemical flow in to the appropriate location in the entrance tank regardless of the corresponding dosing location on the lever arm.
To reduce head loss through the flow control module orifice, a new flow controller is being used in the design. The module being used is a [PT 75 LS|http://floatvalve.com/pt75ls-detail.html] Kerick Valve. This valve was chosen to minimize flow control module size and maximize orifice area. The flow controller will housed in a square tub.
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h5. Figure 2: Flow Controller for Nonlinear module
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