Model of Lassen-H-jort Water Softening Plant

This model represents a plant of the type designed by Lassen and Hjort for softening hard water continuously, on a large scale, by adding reagents that precipitate the bases (lime and magnesia) that cause hardness.

The plant consists of a large rectangular tank divided into four compartments. Supported above the first compartment is a small rectangular tank containing a tilting chamber device for controlling and measuring the rate of flow of water through the plant.

Adjacent to the water feed tank is a semi-cylindrical tank containing the reagents, e.g. milk of lime and caustic soda solutions mixed. By a special device the correct quantity of mixed reagents is discharged at regular intervals into the main tank with each measured quantity of water delivered by the tilting chambers in the water feed tank.

The water, mixed with the reagents in the first compartment of the main tank, passes through the tank to the outlet in the fourth compartment. It has to take a sinuous course up and down through ports and over weirs, passing through two wood-fibre filters on the way. The precipitate settles at the bottom of the first three compartments and is drawn off through sludge cocks.