The Phosphofloatation process removes turbidity and colour from refinery melt liquor. Phosphoric acid and lime are dosed to produce a calcium phosphate precipitate which scavenges colour and this performance is enhanced through the addition of colour precipitant which reduces the colour by 50%.
Screened sugar liquor is pumped from the Untreated Liquor Tank via an automatic flow control valve to a heat exchanger which raises the temperature of the liquor to 85 o C. The liquor then flows to the reaction/aeration tank where phosphoric acid is automatically dosed proportional to the flow rate of the liquor. Lime sucrate is dosed to neutralise the phosphoric acid at a controlled pH of 7.0. Colour Precipitant is added if required to increase the level of decolourisation. The resulting calcium phosphate suspension scavenges colour, turbidity, suspended solids, colloidal and other non sucrose materials.
At the final stage of the reaction tank, specially designed aerator disperses finely divided air bubbles into the treated liquor. On leaving this tank, flocculant is added to the liquor stream proportional to liquor flow rate. The calcium phosphate precipitate forms into large aerated flocs which separate in the body of the clarifier. Clear liquor is taken via a weir box from the bottom of the clarifier, whilst the scum is continuously removed from the surface by rotating rakes. The scum is sent to a de-sweetening clarification process. The clear liquor is discharged to the filter feed compartment of the Deep Bed Filter process.
An automatic control system regulates liquor flow, temperature, pH, reagent dosing and displays these parameters graphically via a trend screen. Alarm systems are activated in the event of variation in parameters.
The addition of process chemicals is controlled by variable speed dosing pumps so that chemical dosing and chemical operating costs can be easily regulated.
In summary, the benefits of the Phosphofloatation process are as follows:
a. Low capital cost.
b. Low operating cost.
c. Readily expandable to meet increased production level.
d. Modest building requirements.
e. Facility to easily regulate process operation and throughput.
f. High brix operation.
g. Reduced energy requirement.
h. Low maintenance costs