Before dosing to the process, powders require high-energy-mixing-1 part powder in 300 parts of water, aged 2 hours.
Powder flocculant dissolution into a useful solution begins with hydration. The powder is quickly wetted in a high-energy chamber. A highly viscous layer forms on the surface of each dissolving powder particle.
This layer shields the non-hydrated polymer inside. High mixing energy is needed to strip this layer away to expose the next layer of dry polymer to the water.
Two solution tanks are required – a mix tank and an aging/working tank.
By the nature of its manufacturing process, the polymer inside the liquid emulsion is already hydrated, greatly simplifying solution preparation and shortening the required age time to 30 minutes.
Specialised emulsions can be fed directly into some processes, but most emulsions fed to most processes require low-energy-dilution of 1 part emulsion in 75-125 parts of water.
Concerns with powders:
Powder flocculant properties vary batch-to-batch and even bag-to-bag within a batch. Powders are commonly referred to as dries when in reality they contain 10-15% water.
Due to the nature of the powder manufacturing process, fines are produced that can dust, creating slipping and inhalation hazards. Coarser particles are often produced that take longer to hydrate.
It is common in actual practice for a significant percentage of the powder flocculant to never dissolve, negatively impacting overall cost performance.
There is often a large difference between the laboratory polymer replacement ratio and that obtained in the sand and gravel wash plant.
The actual replacement ratio of Nalco emulsion to most powders is 1.5-1.75 parts emulsion to 1 part powder. More importantly, there are many additional factors to consider in deciding between an emulsion and a powder.
When comparing emulsions to a powder in the laboratory, careful consideration must be given to the practical side of the application.
Build the following into the decision – normal performance loss, safety, labour costs, and power and capital requirements.
Contrary to what laboratory testing might indicate, and when all of the costs are taken into consideration, Nalco emulsion polymers are frequently more cost effective than powders.
Emulsions are more convenient and safer to handle than powders.