Kayti's Individual Contribution Page

Fall 2009 Contributions

My main focus throughout the Fall 2009 semester with the Chemical Dose Controller Team has been the development and design of a rapid mix tube system for the Agalteca plant. The system developed this semester can also be modified and applied to future AguaClara plants to provide rapid mix of dosed aluminum sulfate with the raw water source. My work this semester has mainly focused on designing this current rapid mix tube system, calculating the head losses experienced through the system and the pipes leading the water to the flocculation tank, and calculating orifice sizes and tube lengths and diameters. I have also worked on designing a system to deliver alum to the center of the tube to allow for an even distribution of chemical across the pipe and small-scale mixing orifices, which is crucial for adequate mixing. A preliminary schematic for a prototype has also been proposed and will be constructed shortly to test the effectiveness and the mixing in the new system. The design of the rapid mix tube system has evolved greatly since the beginning of the semester. I designed the current system to avoid the main problem of the original and second generation designs: the orifice in the original systems was submerged in the bottom of the flocculation tank, making it very difficult to remove the orifice to clean it if clogged or blocked in some way; plant flow would have to be stopped in order to clean this orifice. The current rapid mix tube design consists of two 'stages.' The rapid mix tube again extends up into the entrance tank so that flow to the plant is shut off when it drops below a certain level. On the top of this tube we have inserted a large-scale mixing orifice. Alum is added to the raw water source as it enters this tube through the large-scale mixing orifice, allowing the alum and the raw water to experience large scale mixing in the first section of the tube. Water flows down the pipe, through a length of several diameters of the pipe in order to achieve adequate mixing, then through the next segment of the pipe through a small-scale mixing orifice. This orifice is designed to provide small-scale rapid mixing al the alum with the raw water with a target head loss in mind, allowing the orifice size, significantly smaller than the large scale mixing orifice, to be specifically tailored to each plant and its operating flow rate. From the small-scale mixing orifice, water then flows through the remainder of the pipe, out of the entrance tank through more PVC pipe while encountering a series of bends and straight pipes, where it finally outlets into the bottom of the first channel in the flocculation tank to begin flocculation and continue flow through the rest of the plant. The problem of the inaccessibility of the orifices was solved by locating the large-scale mixing orifice to the top of the entrance tube, easily reached from the top of the entrance tank. The small-scale orifice was also relocated to approximately half-way down the tube in the entrance tank, allowing plant operators to easily access and clean the small-scale orifice should it become clogged.

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