Flocculant Make-down Explained

Definition

Flocculant make-down is the preparation of a dilute polymer solution from dry (or neat liquid) flocculant, ready to be dosed into a thickener or clarifier feed. Dry polymer is wetted and dispersed into water to a target make-down concentration — typically a fraction of a gram up to a few grams of active polymer per litre — then usually given time to age or mature and often diluted further at the dosing point. Two quantities drive the calculation and are easy to confuse. The dry polymer dose is how much polymer is added per tonne of dry solids treated (g/t dry solids). The make-down solution concentration is how dilute the prepared solution is (g/L). The dose sets how much polymer is consumed; the concentration sets the solution flow needed to deliver that polymer. The ProcessConvert flocculant make-down calculator works out the polymer consumption (kg/h, kg/day) and the make-down solution flow (L/h, m³/h) from these — a preliminary make-down and dosing estimate, not a thickener performance model.

Why it matters

Flocculant is expensive and its make-down and dosing system has to be sized for both the polymer mass and the (much larger) solution flow that carries it. Because make-down solutions are very dilute, a small change in make-down concentration swings the solution flow a long way: for a fixed polymer consumption, halving the g/L roughly doubles the solution flow the pumps, mixers, and dilution water have to handle. That is why the dose and the concentration must be kept distinct — one sizes polymer purchase and storage, the other sizes the make-down and dosing hydraulics. Beyond the mass balance, real flocculant behaviour depends on things the calculator deliberately does not model: aging/maturation time for the polymer to hydrate, dilution at the dosing point, water quality (hardness, salinity, temperature), mixing energy (too little and it will not disperse, too much and the polymer chains shear and lose activity), and the actual settling response of the slurry. Those come from vendor data and site settling testwork, not from a make-down sum.

Formula

Units involved

• •dose — g of dry polymer per tonne dry solids (g/t)
• •ṁ_solids — dry solids feed rate in t/h
• •C_solution — make-down concentration in g/L (active polymer)
• •ṁ_poly — polymer consumption in kg/h; m_poly,day in kg/day
• •Q_solution — make-down solution flow in L/h and m³/h
• •ρ_solution — make-down solution density in kg/m³

Concept diagram

Worked example

Common mistakes

• •Confusing the dose (g/t) with the make-down concentration (g/L) — they size different things.
• •Reading the make-down solution flow as a settling-rate or underflow-density guarantee.
• •Ignoring aging/maturation time, so the polymer is under-hydrated when dosed.
• •Over-mixing and shearing the polymer, destroying activity the dose assumed.
• •Forgetting dosing-point dilution and water quality, which change the effective dose response.

When to use the calculator

Use the flocculant make-down calculator to size the dry polymer consumption and the make-down solution flow for a target dose and make-down concentration. Pair it with the thickener underflow density calculator to set the underflow basis, the percent-solids calculator for the feed/underflow solids, and the CCD wash water calculator where the thickener sits in a CCD train. For the dose itself and the settling response, use vendor data and site settling testwork.

FAQ