Current methods of phosphorus production require high phosphoric acid concentrations to produce phosphate salts. These high concentrations are achieved by energy-intensive evaporation processes, and metal impurities such as cadmium are difficult to remove from the phosphoric acid.
The CleanMAP technology enables cost effective production of pure and well-defined mono-ammonium phosphate (MAP) or di-ammonium phosphate (DAP) of technical grade with a cadmium content < 1 mg Cd/kg P (< 0.5 mg Cd/kg P2O5). CleanMAP can be parallel-integrated into an existing production line (Figure 1), replace an existing production line (Figure 2), or be used in new plants.
Figure 1. CleanMAP technology parallel-integrated to an existing production line
Figure 2. CleanMAP technology replacing existing parts in a plant
The technology is based on selective extraction coupled with chemical precipitation. The technology is less dependent on the concentration of the phosphoric acid feed solution, and the main advantage is a reduction of energy demand since there is no requirement for phosphoric acid concentration by water evaporation.
State-of-the-art concentrating of phosphoric acid by water evaporation
To produce merchant-grade phosphoric acid, high acid concentrations are required and in a state-of-the-art system, this is done by evaporating water. Phosphoric acid is normally concentrated in three stages, as shown in Figure 3. The acid from the filter (28% P2O5) is concentrated to 40% P2O5 in a single stage vacuum evaporator. The acid is then clarified to remove precipitated solids and the clarified acid is further concentrated to 54% P2O5 in two stages. The inter-stage concentration is about 48% P2O5. The 54% P2O5 acid is then used for commercial ammonium phosphate production. Concentration of phosphoric acid through evaporation is a very energy-intensive process.
Figure 3. Concentrating phosphoric acid using evaporation
The amount of steam required for concentrating phosphoric acid usually varies between 2.3 and 5 tons of steam per ton of phosphorus depending on production conditions. If the phosphoric acid is purified by solvent extraction the energy demand is about 7 tons of steam per ton of phosphorus. Figure 4 shows the energy cost of water evaporation to concentrate phosphoric acid.
Energy savings of approx 5 ton steam or 5 MW/ton phosphorus (2.2 ton steam per ton P2O5) can be achieved if evaporative concentration is avoided.
Figure 4. Energy consumption for phosphoric acid concentration
The CleanMAP technology renders entire plant sections to be unnecessary such as:
• Steam distribution systems
• Condensation systems
• Cooling water systems
• Acid storage facilities
• De-fluorination systems
Capital costs for the new technology are lower than excluded plant sections.
Reduced maintenance costs are mainly due to the removed need for sludge and scale removal from evaporation systems.
Output from the CleanMAP process
Mono-ammonium phosphate, MAP (technical grade)
- Application, fertilizer on agricultural field or in horticulture, feed ingredient
- Quality, Technical grade 26,5% P (61% P2O5 and 12% N)
- Cadmium content < 1mg Cd/Kg P (Cd < 0,5 mg / Kg P2O5)
- Efficiency in application, very high, the product is fully water soluble and plant available
- Corresponds to CAS-nr: 7722-76-1
Ammonium phosphates is produced in two quality levels, fertilizer grade and technical grade. Fertilizer grade is the large volume phosphorus commodity and contains 21-22% P (48% P2O5), but is not fully water soluble and also contains impurities from the production process (gypsum etc). Fertilizer grade also contains metals in relation to the content in the raw material and can only be distributed to the crop in solid form. The CleanMAP process always produce technical grade MAP (highest quality), which is fully water soluble and can be used for fertilization in solid or liquid form.
Summary of how the CleanMAP technology distinguish itself from state-of-the-art
- All water is removed by evaporation
- Limited to concentrated P streams
- Phosphate salts are concentrated
- Impurities remain in products
- Phosphate is separated from water requiring steam through ion sorption
- Enables processing of dilute P steams (no steam)
- Phosphate salts are precipitated
- Easy separation of impurities becoming resources