Water Treatment - Flocculation 1

[watproc]

Hi,

I am in the process of optimising flocculator paddle speed and cannot find any information regarding paddle direction.

I understand the fundamental process design parameters affecting flocculation performance includes mixing intensity and detention time. G = SQR(P/Vu)

This does not take into consideration alum concentration, the following eqn does: G^2.8Ct = 4.4x10^6

The problem is both of these equations do not take into consideration paddle direction, counter-current or co-current.

Can anybody point me in the right direction?

Watproc

 

[countryham]

I realize that you have to start from "somewhere"... however, any design you attempt ,if it is to be effective on in any system must be relative to the unique system parameters, i. e.---In order to do this --it requires hundreds ,if not thousands of hours at the bench........Rapid mixing time requirement is-- only that time required to bring the flocculating agent in intimate contact with the substrait........The critical time is the amount necessary to bring the flocs together...NOTE.. that in most cases flocs, once formed generally fail to (strongly) bridge together more than once... Then they can become more and more fraigle with agitation .....So, I suggest that you learn how to conduct jar tests on the particular system in question and observe the amount of time (with a stop watch) using ultimate inital agitation (rpms) followed by incrimentally (step)reduced rpms -- and log all data-- with observations----then visualize your bench data as a larger system and then make necessary correlations........Kinda hard to explain thousands of lab/plant extrapolation test I've conducted over thirty five years....Additionally,-- The type of flocculating agent(s) and (time)/(order) of addition is critical........If you want,-- you can call me at (409) 753-9935 to discuss the system and chemistry you are dealing with,,,, Good Luck, Countryham

 

[kenvlach]

Many times the the flow first passes through a small pre-chamber where the flocculant is disbursed with rapid mixing, then the subsequent large residence time chamber is mixed very slowly to bring floc particles together w/o breaking. The latter paraphrases countryham.

 

[semo]

As Countryham said, for optimization, you will need to perform jar tests. A lot of factors come in to play which influence coagulation. Some of them include, pH, nature of turbidity, the type of coagulant, temperature, and mixing.

As you know, after rapid mix, you provide a slow agitation (flocculation zone) which basically brings more particles together in a shorter time. But, you don't want to shear the particles with a high agitation. The velocity of the fluid in the chamber will vary in different locations (ie center of paddle vs. outer edge of paddle). If you are rotating against the incoming current, you will already have a velocity entering that the paddles will push against (increasing the localized velocity). As some flocculators use a back and forth sweeping motion in lieu of a circular motion, this localized velocity increase does little to harm the floc formation as long as it is not too great.

Again, as countryham said, the jar tests will give you a better indication of what will need to be done for optimization. It will be more than just checking the paddle speed. These jar tests should be run on a constant basis also. Running them once and calling it optimized will not be accurate as conditions will change.

 

[RicardoMadrid]

Direction has realy few influence in resaults.
But I use the direction that produce up-flow in the pit to avoid flocs cash agains pit bottom. Therefore rotation direction depend of paddles angle.