Dispersants & Water Reducers
Reduce slurry water demand and, with it, the energy the kiln has to evaporate.
Every kilogram of free water carried into the board kiln must be evaporated — the enthalpy of vaporization of water is 2,257 kJ/kg at 100 °C (NIST). Polycarboxylate ether (PCE) and naphthalene sulfonate dispersants reduce the water-to-stucco ratio required for a given slurry workability. The magnitude of the reduction, and the energy actually saved, depends on stucco chemistry, dosage and line configuration; it is not a fixed number that can be quoted without a plant trial.
PCE dispersants use a comb-polymer architecture: an anionic backbone that adsorbs onto positively-charged hemihydrate sites, with non-ionic polyethylene oxide side chains that produce steric repulsion. Side-chain length, grafting density and backbone charge are tunable. Naphthalene sulfonate (BNS) and lignosulfonate dispersants rely on electrostatic repulsion alone — cheaper, but more sensitive to stucco chemistry and temperature.
A well-matched dispersant lets the mixer break agglomerates and wet hemihydrate crystals at lower water demand. Trade-off: PCE can extend the induction period, which usually needs a compensating accelerator adjustment to keep the knife window intact.
- §NIST Chemistry WebBook — enthalpy of vaporization of water — NIST Standard Reference Database 69
- §Plank, 'Chemical Admixtures — chemistry, applications and their impact on concrete microstructure and durability' — Cement and Concrete Research 78 (2015) 81–99