Flocculation Baffle Box · Technical Reference & Specifications

1. What the baffle box does

A flocculation baffle box is a folded-plate (corrugated-plate) hydraulic flocculator supplied as a modular pack. It is installed in a concrete flocculation basin or channel, downstream of coagulant dosing, where the coagulant has already been dispersed and the particles have begun to destabilise. Its job in that position is not to mix chemicals in, but to keep particles colliding long enough and often enough to build flocs that will settle.

The pack replaces the agitator of a mechanical flocculator with a shaped flow channel. Because the mixing energy comes from the flow itself, the unit needs no motor, no shaft, no gearbox and no electrical supply at the basin.

2. Working principle — where the mixing energy comes from

Water is led along a channel whose walls are formed by plates folded into a repeated V or wave profile. The flow area therefore alternates between a contraction, where the plates converge, and an expansion, where they diverge.

1. Contraction. As the flow area narrows, the water speeds up and the local energy dissipation rate rises. Fast, directional flow brings particles into each other's path.
2. Expansion. As the flow area opens again, the water slows and separates from the plate surface, shedding a train of micro-vortices along the fold.
3. Repeated contact. Each fold repeats the cycle. A single pass through a folded-plate channel therefore subjects the water to many successive cycles of acceleration, eddy formation and deceleration, rather than to one bulk stirring action.
4. Secondary circulation in the troughs. The folds also set up circulation cells across the channel section, which continually exchange water between the core of the channel and the slower layer at the plate surface, so no stream of particles travels through the basin untouched.

The practical consequence is that the same collision frequency can be reached at a lower mean velocity than in a flat-walled channel, and the mixing is generated precisely where it is needed rather than throughout the whole basin volume.

3. Stage arrangement — shear that decreases as the flocs grow

Floc formation has two requirements that pull in opposite directions. While the particles are small, the water must be mixed hard enough that they meet. Once the flocs have grown, the same intensity of mixing tears them apart again, and the fragments settle poorly. A folded-plate basin resolves this by splitting the flocculation channel into successive stages with a decreasing velocity, so the mixing energy falls stage by stage along the flow path.

• First stage — vigorous mixing. The plates are arranged so that the flow is repeatedly contracted and expanded, producing the most intense micro-vortex field of the train. This is where coagulant-destabilised particles are driven into contact and the first flocs appear.
• Middle stage — moderate mixing. The same folded geometry is retained but the flow velocity is lower, so flocs continue to grow in a gentler eddy field without being broken up.
• Final stage — gentle, near-uniform flow. Mixing intensity is reduced further, so that flocs arrive at the outlet intact and uniformly suspended, ready to settle in the following sedimentation zone.

The number of stages, the fold angle and the velocity used in each stage follow from the basin dimensions and the process design, and are confirmed per project. They are not fixed catalogue values: two basins built from the same module may use different stage settings.

4. Comparison with other flocculation arrangements

This comparison is qualitative and generic to the three arrangement types. It is not a performance guarantee for any particular basin or water quality.

5. Specification status

We publish only the figures we can confirm for a specific order. The values below are fixed against your basin drawing and process design, then quoted on request — they are not catalogue constants.

6. What we need in order to quote

Send the following and we will come back with the plate arrangement, module dimensions, material, quantity and export packing for your basin:

• Basin or channel drawing, including internal dimensions and the available water depth.
• Design flow, and whether it is constant or varies over the day.
• Water source and quality: influent turbidity or suspended solids, temperature range, and pH range.
• Coagulant and dosing position, so the baffle box is placed where the flow has already been dosed and dispersed.
• Target velocity gradient and flocculation time, if your process design has already fixed them; if not, tell us the target settled-water quality and we will work from that.
• Whether the unit is for a new basin or a retrofit of an existing mechanical or baffled flocculator — retrofit units are made to the opening dimensions you actually have.
• Material preference and any chemical or abrasive content in the water that affects the grade.
• Destination port and quantity, for export packing and freight quotation.

7. Installation, operation and maintenance

• Placement. Modules are installed in the flocculation zone between the coagulant dosing point and the sedimentation zone. The pack is fixed to the basin wall or floor, or carried on its own frame, so that it cannot be displaced by flow or by basin draining and cleaning.
• Alignment. Flow must enter each stage along the channel axis. Bypass gaps at the sides, floor or top of the pack allow water to travel around the plates instead of through them, which reduces the mixing actually seen by the flow — the openings are closed off at installation.
• Operation. There are no settings to adjust in service: the mixing intensity is fixed by the installed geometry and by the flow rate through the basin. Operation therefore depends on keeping the design flow and the dosing rate within their intended range.
• Maintenance. Inspection is visual. Plates are checked for accumulated debris and for mechanical damage after basin cleaning or after any work in the basin. Cleaning is by water jet and hand brushing; no lubrication and no spare drive parts are required.
• Basin draining. Where a basin is drained periodically, the packs are designed to be lifted out as modules if the plates need to be inspected or replaced off-site.

Note on figures

Figures in this reference describe the folded-plate flocculation method and the items we confirm per order. Dimensions, fold angle, plate thickness, stage velocities, velocity gradient, flocculation time, head loss and design flow are established from your basin drawing and process design, and are quoted on request. Send your drawing and water quality data and we will confirm them for your project.