Sedimentation Tank Dimensions Design Program

The design of the sedimentation tank is a critical piece of the design of the entire plant. Its properties, such as depth and critical velocity, are important in determining the dimensions and lamella spacing. This program requires inputs from the user and from our basis of design in order to determine the design and dimensions necessary to generate the AutoCAD drawing and design report.

Sedimentation Tank Design Program Algorithm

Sedimentation Tank Inputs
Sedimentation Tank Outputs
Sedimentation Tank AutoCAD Drawing Program

Algorithm

The sedimentation program calculates the dimensions of one sedimentation tank considering the dimensions of inlet slopes, sed plate frame, lamella, sed launder, as well as dimensions of the inlet channel.

Firstly, the design of sedimentation tanks for a given flowrate Q, involves a selection of the number of sedimentation tanks from a user input. Based on the user input, the flowrate in one sedimentation tank and length of the sed tank are calculated:

and

where the width of the sedimentation tank was set to 42.5 inches, which represents the width of available lamella material, and the upflow velocity was set to 70m/day to allow for possible sludge blanket formation.

The wall height of the sedimentation tank was set to be equal to the height of the water level plus the height of the freeboard of 10cm. This plant freeboard is a design assumption used through out the design algorithms to give a buffer to allow for possible variation in water levels without resulting in tank overflow.

The water level height is calculated as the sum of elevation of the sed slopes, 2*outerdiameter of the pipe used for the sed plate frame, height of the lamella, height of the water above lamella, and the distance between the top of the slopes and the bottom of the lamella. Two other factors also taken into consideration are the thickness of the concrete ledge used to hold up the launder on the inlet channel side and the extra space between the top of the lamella and the launder to offset any error during construction. Because of these two variables there is significant space between the top of the lamella and the launders, which results in an increase in the height of the water in the sedimentation tank, leading to a taller sedimentation tank.

where, the elevation of the sed slopes is defined as:

The calculations of the lamella height can be found here.

The launders leaving the sedimentation tanks were designed in a similar manner as the sedimentation sludge drain manifold. The height of water above plate settlers has been defined as:

The calculations of dimensions of the inlet channel can be found here.

Finally, therefore:

and

Sedimentation Drain Design

Drain Sizing

The time it takes to drain the sed tank can be approximated by:

where

A function to determine the valve diameter iterates from the smallest possible diameter to the largest diameter, calculating the respective drain times using the time function. The valve diameter function returns the smallest diameter that allows the sedimentation tank to drain within the time defined by the user. The iteration stops once a time no greater than the desired time.

Couplings

The nominal valve diameter is the inner diameter of the slip side of the adapter, and is used to calculate the outer diameter of the slip side. The nominal diameter is also the outer diameter on the threaded side which will be used as the inner diameter for the valve that fits it.

Drain Slopes

Since the center of the valve is aligned with the floor of the sedimentation tank, slopes are required in the floor of the tank. The slopes have a width equal to the diameter of the valve and a depth equal to half the diameter (placing the center of the valve at-grade) with a slope of 30 degrees.

Gate Valves

Gate valves are placed in every bay of every sedimentation tank at-grade to allow for draining.