Chemical Dose Controller History
By far, the biggest hurdle in the development of AguaClara technology has been devising a method for accurately and precisely administering process chemicals while adhering to the fundamental AguaClara design constraint of creating solutions which do not rely on electricity. Modern water treatment plants have computerized control and precise metering pumps at their disposal and while an AguaClara engineer has neither of these, this does not diminish the need for accurate metering.
To that end, AguaClara engineers have been developing a Chemical Dose Controller (CDC) which utilizes principles such as gravity, differences in head pressure, major losses in pipes, etc. to predictably meter process chemicals. The first CDC developed by AguaClara engineers was the Linear Dose Controller, named so because of the linear relationship that exists between flow and the head-loss that occurs as fluid flows through a pipe. This was a simple design that utilized the predictable major head-loss which occurs in a small diameter pipe to meter the flow, and therefore the chemicals, administered to the plant. This relation only holds true under laminar flow conditions and therefore fails as plants increase in size because the required increase in chemical delivery rate causes the fluid to enter the turbulent range.
To overcome this, AguaClara engineers are developing a CDC that utilizes the head-loss through an orifice (rather than through a pipe) to meter the flow of process chemicals. This is the Non-Linear Dose Controller, so-called because flow is now a function of the square-root of the height differential, making the relationship non-linear.
Current State of the Nonlinear Dose Controller
The AguaClara engineers from academic year 2009/10 not only designed, but built and installed a Non-linear Dose Controller (NDC) in a new AguaClara plant in Algateca, Honduras. The current NDC is installed on top of the entrance tank of the plant and consists of a float connected to one end of a lever arm and the dosing orifice connected to the other end.
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(Inset figure of current CDC) The entrance tank is connected to the hydraulic flocculator by way of a rapid mix orifice. A change in flow rate through the plant is indicated by a change in the level of the entrance tank. This is transmitted to the lever arm by way of the float. For example, if the flow rate of the plant were to decrease from 100% to 80%, the entrance tank would drop by a proportional amount. Since the pivot is in the center of the lever arm each centimeter of change in the entrance tank will correspond to a centimeter of change in the heights of both ends of the height of the lever arm (although, obviously, the two ends will be moving in opposite directions).