Abstract
The High Flow Dose Controller aims to provide a simple dose controller for AguaClara plants that requires minimal input and oversight from the plant operator. In keeping with AguaClara standards, this dose controller will not require the use of electricity, will be simple to understand and operate and will be constructed from robust components. The High Flow Dose Controller will be designed for use with flow rates where the Liner Dose Controller is unable to meet flow demands.
Introduction
One of the biggest hurdles in the development of AguaClara technology has been the development of a method to administer process chemicals that is both accurate and simple to operate.
The Linear Dose Controller (provide hyper link to this web page) was developed by AguaClara engineers and is currently used in AguaClara plants. The underlying principle utilizes the relationship between head-loss and laminar flow through a small diameter tube to accurately meter process chemicals. The LDC provides a simple design that has been well received by plant operators. As design plant flow rates increase, however, maintaining laminar flow in the small metering tube leads to somewhat cumbersome solutions (e.g. extremely long tube length, excessive number of tubes).
To overcome this shortfall AguaClara technology requires a dose controller whose flow mechanism can be predicted over a wide range of flow conditions. This controller must maintain a relationship between head and flow that can be matched to the relationship between flow and water elevation of the entrance tank. Both constraints can met by the predictable flow rate through an orifice.
Flow through an orifice (Q) is related to the area of the orifice (A) and the square-root of the height (h), corrected for vena-contracta, Kvc. This equation holds true under both laminar and turbulent flow conditions.
Previous design work in this area led to the development of the Non-Linear Dose Controller (provide hyperlink to this page). This device was a simple design utilizing an orifice whose height, and therefore chemical flow, could be adjusted via a slide on a lever arm. The lever arm was coupled to plant-flow via a float in the entrance tank which was coupled to the plant via an exit orifice. This meant the head loss through the entire plant was reflected by water level changes in the entrance tank. This design led to an unexpected failure when accumulated grit in the flocculator was reflected by an increased water level in the entrance tank which led to an increase in chemical flow rate. Other challenges with this design include surface tension losses in the orifice at particular flow rates and imprecise (unrepeatable between units) orifice manufacturing techniques.
The High Flow Dose Controller (HFDC) will investigate a new approach to metering process chemicals through a needle valve, thereby providing a variable orifice for dose control. A new method to couple the entrance tank to the plant will be developed.