Abstract
The linear nonlinear dose controller is being designed for plants with high flow rates. 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 . This creates a linear relationship between height of water in the grit chamber and the flow of alumto maintain a constant chemical dose with varying plant flow rates. For high plant flow rates, the flow rate of alum will be turbulent. 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 flowrates. To get around this issue, it has been determined that the flow rate to height relationship in the entrance tank can be nonlinear so long as the alum has the same nonlinear relationship. For example, Furthermore, headloss through the flowcontrol module is excessiviely high.
The nonlinear doser uses an orifice to control the relationship between changing plant flow rates and chemical dose. The weir entering into the rapid mix is also an orifice and the plant and chemical flows vary in direct proportion. 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 if water flows from an orifice in the entrance tank to rapid mix, then alum must flow through a similar orifice, so that they have the same relationship. We decided to achieve this by having the doser consist of a large pipe that moves with the fluctuations of the water in the entrance tank. Since the pipe diameter is so large, major losses can be neglected, and we are essentially moving the location of the orifice up and down, creating different elevation heads.
Since the focus of the CDC team was shifted to design, this aspect of the project has been put on hold temporarily.