Nonlinear Chemical Dose Controller

Abstract

The nonlinear dose controller will need to be used for turbulent flow in the chemical doser tubing. The previous chemical doser design requires that the alum flow be laminar. The Linear Chemical Doser uses the relationship between laminar flow and major losses in the doser tube to maintain a constant chemical dose with varying plant flow rates. When the flow in the tube is turbulent the linear relationship no longer exists and a nonlinear dose controller is necessary to maintain a constant chemical dose with variations in flow rates.

The advantage to designing a nonlinear CD is that higher chemical flow rates can be used. The limit of the current flow control module is 400 ml/min. This has been adequate for the plants currently in operation (La 34, Ojojona, Tamara, Marcala and Four communities). As the demand for larger AguaClara plants becomes an issue, larger chemical dose flow rates will be required. Furthermore, head loss through the orifice entering the flow control module increases as chemical flow rate increases. This requires the chemical stock tank to be elevated to an unreasonable height.

The nonlinear doser uses an orifice instead of a dosing tube to control the relationship between changing plant flow rates and chemical dose. The rapid mix entrance is also an orifice and the plant and chemical flows vary proportionally to each other. Design work is being performed to determine if this idea is feasible. The relationship between chemical dose and turbidity will be changed manually as it is in the linear doser.

Methods

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 Kerick Valve. This valve was chosen to minimize flow control module size and maximize orifice area.