Horizontal Flow Flocculation Design Program

*THIS PAGE IS UNDER CONSTRUCTION WHILE THE HORIZONTAL FLOW PROGRAM IS BEING CREATED. PARTS OF THIS PAGE ARE LIKELY TO CHANGE**

This flocculator program determines the size, number, and spacing of the flocculator channels and baffles, based on the results of the Computational Fluid Dynamics (CFD) team and the specification of horizontal flow. Horizontal flow is used for very high flow rates to avoid building the plants even taller, instead making them wider. Horizontal flocculators are also easier to drain than vertical flocculators made of cement baffles because individual drains are not needed for every lower baffle as they are in the vertical flocculator. The tank is designed given an optimal energy dissipation rate to mix the alum (coagulating chemical) with the incoming water and to maximize the opportunity for flocs to form.
The program also outputs arrays of the location of each baffle in the tank; these arrays are used by the AutoCAD scripts to draw the baffles in place in the flocculator.
The programs used are Flocculator 3 Horizontal w Standard Vars JP (the design program) and floctank (the autoCAD script). In the scheme of the whole plant, the flocculation tank is drawn after the sedimentation tank (so many of our variables are constrained by an already-drawn sedimentation tank). Eventually the design program from horizontal flow will be integrated into the same program used to design vertical flow flocculators. The program will decide whether to use vertical or horizontal flocculation based on the flow rate. ADD EQUATIONS

To create a consistent relation between vertical and horizontal flow, generic notation is used. Tau represents the distance to turn. The flow area, which is the cross sectional area that is perpendicular to the flow of the water, is Rho*S.

Top View

COMING SOON

Front View

COMING SOON

Flocculation Design Algorithm

Each section outlined below corresponds to its equivalent MathCAD code, identified by the same titles.

 -To view the first part that informs and establishes the equations and design ideas used in the actual drawing of the tank refer to the Energy Dissipation Flocculation Design Program page as these equations and ideas are the same.

 -The second part determines the number, spacing, energy dissipation, and collision potential of the necessary baffles.

 -The third part determines the width, height, size, and the other parameters needed to draw the flocculation tank with the baffles inside it.  This section is heavily relied upon by the MathCAD code in floctank that draws the plant.

 -The last part creates and outputs the matrix of baffle positions.

Flocculator Functions

The critical balance in the flocculator is between ensuring that the alum and entering water are meeting the energy dissipation (ED) and collision potential (CP) goals, and not breaking up flocs that have formed.

Calculating the amount of baffle spaces that give the target ED rate is done with a non-iterative code (as opposed to the vertical code which is iterative). The optimal Tau/S value of 3 found from the CFD calculations can be used for horizontal flocculators since the flocculator can be made as wide as necessary (whereas in vertical flocculation, Tau was constrained by the height of the sedimentation tank), so iteration is not needed.

The number of spaces per channel is determined by a non-iterative code also since the length of the channels are fixed to be the length of the sedimentation tank. Unlike in vertical flow flocculation, channels will always have an odd number of spaces to ensure that water flows into successive channels and eventually into the sedimentation tank.

Calculation of Flocculator Geometry

The height of water at the end of the flocculation tank is set to be the same as the height of water at the beginning of the sedimentation tank, i.e. no head loss occurs between the two:

The "height" of the floc channel is equal to the height of a vertical flow tank, therefore

The number and spacing of floc spaces and floc baffles is calculated, as well as the CP, for the specific tank being drawn. The minimum number of floc spaces is 1, which is if there are no baffles, and the maximum number of floc spaces is determined using the following Floor function which forces the number of spaces to be an odd integer:

When calculating the max, L represents the length of the sed tank L.Sed and T represents the thickness of a baffle T.FlocBaffle. To get the maximum number of floc baffles, S is taken as the minimum floc baffle spacing S.FlocBaffleMin. However, to get the minimum number of floc baffles, S is taken as the entire length of the flocculator, which would signify that there are no baffles.

The center-to-center distance between baffles includes the spacing between baffles and the thickness of the baffles, for each channel. This is an array with an element for each channel, as each channel may have different baffle spacing.

The residence time in the flocculator is determined as follows:

The height of water at the beginning of the flocculator is based on the height of water at the end of the flocculator (which is the same as in the sedimentation tank), plus the headloss through the flocculator. The head loss is determined per baffle (and per channel, and in the whole flocculator) using the HL function in the fluids functions program. An additional 10 cm of freeboard space was added to the water level (HW) found at the beginning of the flocculator to determine the height of the flocculator walls.

The head loss per baffle in each channel:

Water flows between channels in the flocculator through ports cut in the concrete. The area of these ports is determined to ensure flocs will not be broken up. The width of these ports may vary by channel, as the baffle spacing may be different from channel to channel.
The energy dissipation rate through the ports is set to be same as around the baffles; the dimensions of the port are calculated to be the same as that of the baffles.

The width of these ports is set to include the thickness of the concrete lip needed to hold the baffle in place. It should be noted that this lip needs to be taken into account when determining baffle spacing for smaller plant when this length loss becomes significant.

Position Calculations for Each Baffle

The length of the lower floc baffles and upper floc baffle that was seen in vertical flow is now technically the left and right baffle (both are on the same height level). These baffles are set to line up with the top of the tank rather than the water level. The baffles are oriented to switch from one side of the tank channel's wall to other ("east" to "west") so that the flow of water is smooth back and forth through the tank.

Length of "Lower" Baffle = Length of "Upper" Baffle:

The placement of the baffles in the flocculator is determined by algorithms that create a matrix of baffle displacements from the end of the flocculator (see this drawing program for step-by-step details of how the lamina, baffles, slots, and other tank details are drawn). All baffles are also placed at the bottom of the tank, which is represented in a Z-matrix for the baffles.

The width of the baffle must also be determined.