NFC-IET-MULTAN

SSP - Nutritional Solutions to Sustainable Yields

Sulfur demand of crops can be met by Using Fertilizers like Single Super Phosphate

DAP is dependent of Global Phos Acid suppliers and availability depends on global swings

SSP could easily meet P requirement while simultaneously supplying S, Ca and micro–nutrients to Crops

SSP also helps to protect the soil from disintegration

SSP use in Sulphur deficient crops increases the crop yield by 15-25%

SSP MANUFACTURING PROCESS Raw Material

The phosphate rock, imported from Nauru, Jordan and

Morocco is mainly fluorapatite, Ca5(PO4)3F and is

equivalent to 70 - 85% Ca3(PO4)2 by weight.

The actual composition of the phosphate rock varies with

the source.

The sulfuric acid is produced on the site.

The reactions occurring during the production of single

superphosphate are complex and are

usually summarized as follows:

1. Ca5(PO4)3F + 5H2SO4 → 5CaSO4 + 3H3PO4 + HF

2. Ca5(PO4)3F + 7H3PO4 + 5H2O → 5Ca(H2PO4)2

.H2O + HF

These reactions can be combined to give the overall equation:

2Ca5(PO4)3F + 7H2SO4 + 3H2O → 7CaSO4 + 3Ca(H2PO4)2 + H2O + 2HF

The production of superphosphate consists of three

distinct steps.

Step 1 - Phosphate rock blending and grinding

Step 2 - Superphosphate manufacturing

Step 3 - Granulation

Step 1 - Phosphate rock blending and grinding

Phosphate rock from different sources have different

phosphate, fluoride and silica contents. These rocks are

mixed in the blending plant to produce a product with a

total phosphate concentration of 15%. The phosphate rock

mixture is passed through a hammer mill which reduces

the particle size to 0.5cm or less.

The coarsely ground rock is then passed through an air

swept roller mill (Bradley Mill) to attain a rock grist of

approximately 75% less than 75 microns. The powdered

Step 2 - Superphosphate manufacture

The ground rock and sulfuric acid are reacted in a

horizontal mixer. The feed rates are approximately:

Phosphate rock - 25 tonnes/hour

98% Sulfuric acid - 14.5 tonnes/hour

Water - 6 tonnes/hour

A continuous flow of the sloppy mix drops out of the mixer into the

Broadfield Den.

The den consists of a slowly moving floor (approx. 300 mm/min)

to enable setting of the cake and reciprocating sides, which

prevent the superphosphate adhering to the walls. The partially

matured superphosphate cake is cut out of the den with a rotating cutter wheel after a retention time of approximately 30 minutes.

Step 3 - Granulation The granulation process is important in producing

superphosphate of the required physical properties.

The granulation circuit consists of a pulveriser, granulation

drum and classifier. The pulveriser breaks up any lumps in the

product before it is fed to the granulation drum. The

granulation drum rolls and agglomerates the superphosphate to form granules.

The incline of the drum and the feed rate determine the

retention time and bed depth. The granules are passed

out of the end of the drum and through a classifier (wire

screen).

Oversize granules (>6 mm) are recycled through the drum

via the pulveriser while the finished product is conveyed to the product stores.

The superphosphate continues to cure in the store for

about two weeks and the product is dressed (oversize is

passed through a hammer mill after screening) before

dispatch.

ENVIRONMENTAL IMPLICATIONS

The most significant potential environmental hazards are

dust (from the grinding of phosphate rock) and gaseous

hydrofluosilicic acid (from the reaction between

hydrofluoric acid and silica or quartz) emissions. These

are both carefully monitored, and a dust catcher and gas scrubber are used.