Chemical Dose Controller Reflection Report
Authors: Eva J Romero Luna and Hersh Sangani
AguaClara Reflection Report
Cornell University
School of Civil & Environmental Engineering
Ithaca, NY 14853-3501
Date Submitted: 24/09/2010
Abstract
The Fall 2010 Chemical Dose Controller (CDC) team has gone over previous reports and calculations for the dose controller to selectively choose information pertinent to the CDC project and relevant to our semester goals .
Our goals are to become familiar with the apparatus, design parameters and constraints, to design a Constant Head Tank that can be scaled up or down for a given plant flow rate and to create appropriate databases for the materials used (i.e.: float valves, frame). Also, we would like to improve the design so that it will incorporate the different chemicals used in the plant.
Keywords: Non-linear Chemical Dose Controller, Constant Head Tank, Float valve, chemical compatibility.
Introduction
The current Non-Linear Chemical Dose Controller design is limited to plants with small flow rates mainly because of the sizing of a key component which is the Constant Head Tank (CHT). The CHT is needed to maintain a constant alum dosage even when the plant flow varies; it maintains a constant dosage by means of a float valve. The current CHT design consists of a 1 L plastic tank with two orifices and a mini float valve. For Fall 2010 semester, the CDC team will be designing a CHT that can be scaled up for bigger plants by changing the size of the orifices depending upon plant flow rate.
The CDC is based on the non-linear relationship between flow rate and head loss:
(1)
Where Q = flow rate
Kvc = Vena Contracta coefficient.
∆H = Head loss
Area = area of orifice
To address, for example, an increase in plant flow rate, this relationship will again be used to determine the orifice sizes on the Constant Head Tank. A change in orifice size will also define which type of float valve is used; therefore, a float valve database will be created.
Another task for Fall 2010 team will be to create a construction material database for the frame of the CDC that is compatible with the chemicals used in the plant, the current frame material is easily eroded by the alum leakages from the stock tank and cannot be found locally in Honduras.
Experimental Design
Our current design for the constant head tank cannot accommodate the higher flow rates of the new plant . Therefore, we need to design our apparatus to allow for higher flow rates of alum. One way to accomplish this is to increase the height difference between the stock tank and the constant head tank. Another way is to increase the diameter of the tubes connecting the stock tank to the constant head tank and the constant head tank to the NDC . Since increasing the height of the stock tank only increases flow by the square root of the height (1), we think it is more feasible to adjust the tubing, which increases flow rate in proportion to the diameter . Our experiment is to test different diameter tubes on the constant head tank in order to increase flow rate. An additional way of changing the flow of alum going into the entrance tank is to change the orifice. We will also calculate, using different orifices sizes, increase in flow rate to the desired stock flow rate for the new Honduras plant.
First we will calculate the ideal tube diameter. Then we will research the different tube sizes that we can use and decide on which ones we want to work on. Before testing them, we will calculate the theoretical values of the flow rates for each tube. Then we will conduct a series of tests to measure the flow rate and compare them to our calculated values.
We will also need to use a new float valve to accommodate the larger flow rate of alum. We will identify the different float valves that could possibly work with our new Flow Controller design and then test them once our new tube/orifice designs are implemented.
Future Work
For the next two weeks we hope to conduct our experiments on increasing the flow rate of alum. The only thing that might prevent us from completing this goal is if we cannot get the parts we need in time. In that case we can at least have our experiment planned out and ready for when what we need arrives.
Once we have addressed the issue of accommodating a large plant flow, we then need to look at all of the materials being used in the whole CDC and research ways to find cheaper or more accessible materials. The first step in this is to organize the materials into a database and then look at each one to see if we can find something compatible and cheaper without sacrificing the quality of the material.
We also want to look into combining the CDC with the other chemical flow devices. This would possibly make it easier for the plant operator to do his job.