Bitumen emulsions are usually made using a colloid mill, although other dispersion devices are possible. In the colloid mill energy is applied to the system by passing the mixture of hot bitumen and water phase between a rotating disc, cone or flywheel and a stator. The rotor as well as stator may be grooved or have teeth in order to create a turbulent flow.
Bitumen emulsion can be produced either in a batch or an in-line process plant. The batch process involves at least two process stepswater phase (soap) preparation and the actual emulsion production. The water phase is prepared in a tank into which heated water, emulsifier and other emulsion chemicals are metered and the solution properly mixed. In the emulsion production process the bitumen and the pre-made water phase are dosed to the colloid mill. If solvent is to be added to the bitumen, then a batch tank is needed for bitumen as well, or the solvent must be dosed in-line.
In the batch plant the emulsion production itself involves only a few material flows, which allows manual process control. However, proper metering of the various components are decisive for the quality of the emulsion and automatic or semi-automatic control will make the manufacturing more efficient and reduce human error.
Furthermore, the chemicals used may be hazardous as well as corrosive, which means closed dosage systems rather than open tanks and portable pumps are preferable in order to ensure safe work and environmental conditions.
In the in-line process the water heating and all material dosage are done continuously using individual dosage pumps for each material. No batch tanks are used. Instead, the water phase system must further be designed to provide sufficient reaction time for the chemicals so that adequate neutralization and solution take place before the water phase meets the bitumen.
The process needs to be automatically controlled using flow meters for all material dosage except acid, which should be controlled by the pH in the water phase. Various special additives such as latex, SBS or bitumen dope may be used and will then require special components and technical solutions. Latex for example is shear sensitive and may coagulate in pumps and lines. SBS modified bitumens usually require the emulsion to be produced above the boiling point of water, which requires production under pressure and cooling before release to atmospheric pressure in the storage tank.
