Good polymer mixing or injection methods for dewatering sludge? 1

[USAeng]

We use polymer at our plant for dewatering sludge in belt filter presses and centrifuge.

For our presses we currently take neat polymer in liquid form and mixing with non potable water in an old Dynablend L6-P mixer which then gets pumped into fiberglass storage tanks. From there the polymer gets pumped into a small pipe to a single 90° injection point in the sludge piping approx. 100' from the belt filter press.

Our centrifuge (for dewatering digested sludge) - polymer gets mixed with potable water in a separate tank by a similar Dynablend mixing system. That mix gets pumped from the tank to the centrifuge and gets injected into the sludge stream right before entering the centrifuge.

Today I am beginning the project of looking at new systems and ideas to make our operation better. Does anyone here happen to have good experience with polymer systems? Thanks

 

[bimr]

I am familiar with the setup. Quite common and seens to work well.

 

[USAeng]

Thank you for the response.

I'm looking for any thoughts, tricks, equipment etc to become more efficient if there is anything.

I see a wafer style injection piece that might be a better way to inject into the piping?

 

[bimr]

The type of mixing equipment required will vary, depending on the selected polymer, viscosity, and solids characteristics. Before injection, polymers are mixed into a dilute solution between 0.25 and 0.50 percent by weight. A metered, water supply connected to the mix tank discharge is recommended to further dilute the polymer solution and thoroughly disperse the polymer into the solids

Polymer addition usually occurs via injection through a multiport injection ring; it is mixed with the sludge as it flows through an inline mixing device. In some cases, the polymer may be mixed mechanically in the retention tank. However, this generally results in higher polymer consumption.

Mixing energy is the energy required to instantaneously mix the polymer with the suspended solids of the slurry. The optimum mixing energy is usually determined on-site by adjusting the throat opening inside the variable orifice mixer. For example, to increase the mixing energy, reduce the throat opening of the mixer by increasing the adjustable counterweight and turn up the adjustable bolt on the valve stop handle to allow the weight arm to move further down. Too little or too much mixing energy results in less than optimum floc formation that adversely affects thickening action.

The disadvantage of a wafer style is that there is no adjustment of the mixing energy, except for flow rate. Since the amount of mixing energy is important, a preferred solution would be a mixing valve where you can adjust the energy.

The location of the polymer injection points also requires careful consideration. The design, generally, will allow polymer feed directly into the solid bowl centrifuge and/or upstream of the centrifuge, either before or after the feed pump. Maximum flexibility is needed to allow future modifications of the system. Design considerations include pilot testing a range of polymer
concentration.

 

[USAeng]

Thank you very much for this information!