Ammonium nitrate based fertilizers granulation

 

CEAMAG and "HICAP SPHERO" process

  • Simple flow-sheet which reduces investment and makes the process easy to operate and maintain,
  • Low recycle ratio (typically 2.0 to 2.5/1) giving low CAPEX and OPEX,
  • Optimised air flow rate through the spherodizer, leading to optimized scrubbing system and energy consumption,
  • Superior product quality with high granule hardness, high bulk density and incomparable shape,
  • Respect of most stringent applicable norms for pollution control.

In the production of AN based fertilizers, the granulation technologies are nowadays preferred for new plants and tend to replace the prilling processes in existing ones, in regards with major advantages:

  • Granulation processes allow the production of bigger granules than those which can be obtained with the prilling processes,
  • The mechanical properties of granules are in general better (mechanical strength, bulk density),
  • The investment and operation costs are lower, compared with plants having the same obligations of pollution control.

The spherodizer drum granulation brings additional interests because of the so called “onion skin” granulation process, leading to optimal hardness and roundness of products.

The “HICAP SPHERO” process is a melt granulation process based on “onion skin” granulation, applied to production of a wide range of Ammonium Nitrate based fertilizers, as for instance:

  • AN 33.5,
  • CAN upwards 20%N content,
  • ANS 24 to 26% with Ammonium Sulphate,
  • ANS with gypsum,
  • ANS with gypsum and Ammonium Sulphate.

The originality of the technology consists in using the principle of spherodizer with specific inner parts fed in specific conditions which allow getting directly the product having its final properties in term of hardness, humidity, density and roundness.

The “HICAP SPHERO” process has been successfully applied since 1990 in two 1500 mtpd granulation units in Tertre, Belgium for producing AN, CAN and other AN based fertilizers.

Granulation process

Raw materials, recycling of solution from the gas scrubbing section, dusts from cyclones, inert material and additives as the case may be are sent to an agitated slurry tank under flows and residence time controls.

The granulation and drying of the product are achieved in a single rotating drum (the spherodizer). Conditions of spraying of the liquid feed and recycling loop control are the heart of the process and the keys for the stable and optimized operation.

The inner parts of the spherodizer are designed for optimization of the operating conditions and duration of production runs.

Raw material control

During production of CAN type fertilizers, the very short residence time in the slurry tank and ammonia excess allow the control of CN formation from calcium carbonate contained in the dolomite filler material, which is an important factor for the behavior of products during the storage.

Recycle Ratio Control

Due to the high efficiency of the granulation principle, in a spherodizer, it is easy to achieve a stable growth pattern of the granule size. To this effect, it is necessary to maintain a selected stable amount of recycling which provides the seed required for granulation and the basis for the equilibrium of the energy balance. Accordingly, the solid recycle to the spherodizer is composed of fines from screens, crushed over-size granules from the crusher and part of the on-size granules production. Reliable crusher operation and efficient screens are thus important for the optimization of the recycling ratio and a high production rate.

Product cooling

Ammonium Nitrate has crystal transition points at 84 and 32°C (except when these points are changed by additives). Cooling shall normally take the product to – under design conditions – below 32°C.

It is proposed to use a plate/plate cooler, where cooling of the product is achieved in a bulk flow heat exchanger and where the cooling medium is water. This system offers an energy efficient cooling process and air volumes are minimised in the plant.

The cooling process will be designed in a way that the product is cooled directly through all temperature transition points for AN in order to avoid thermal cycling in the product during the cooling operation. The residence time will be sufficient for all phase transitions to take place during the cooling process.

Scrubbing system

A scrubber system is installed for elimination of dusts and ammonia, in respect with EFMA-BAT recommendations or other applicable local standards.

The scrubbing solution is fully recycled to the Slurry Tank. The plant thus does not generate liquid waste in normal operation.

 

Single train typical productions
  AN 33.5 CAN27 ANS24
1 Raw materials efficiency >99.9% >99.9% >99.9%
2 Water content ≤ 0.3% ≤ 0.3% ≤ 0.3%
3 Granulometry (*) 90% min 2.5 to 4.5 mm
d50 : 3.4 mm
90% min 2.5 to 4.5 mm
d50 : 3.4 mm
90% min 2.5 to 4.5 mm
d50 : 3.4 mm
4 Hadness (for granules 3.4 mm) 4.0 kg 5.0 kg 5.0 kg
5 Utilities (per ton product)      
Electrical power (kWh/t) ~22 kWh/t ~22 kWh/t ~22 kWh/t
Steam (kW/t) ~51 kW/t ~51 kW/t ~51 kW/t
Nominal capacity per single train 380 000 mtpa 560 000 mtpa 500 000 mtpa
Pollution control      
Ammonia in atm. <30 mg/ Nm3 <30 mg/ Nm3 <30 mg/ Nm3
Dusts in atm. <30 mg/ Nm3 <30 mg/ Nm3 <30 mg/ Nm3
Liquid effluent No liquid effluent No liquid effluent No liquid effluent

(*) Typical: can be adapted to customers request for smaller or bigger granules.

Process Description

Raw materials feeding

Solid raw materials necessary for the required production are received from battery limits into separate bins and are extracted at a controlled rates by means of weighing belts and dosed to the Slurry Tank T203. The solids are then pre-mixed with AN-solution arriving from the battery limits under a controlled flow rate. The ammonium nitrate flow is chosen as the flow controlling the production rate of the plant and addition of solid raw materials.

The Slurry tank is stirred and maintained homogeneous by the Slurry Tank Agitator A201 and heated by an inner coil fed with steam. The tank also receives the dust from the dedusting system and diluted ammonium nitrate solution from the scrubber.

A small amount of ammonia is injected under flow control in the tank for controlling the pH in the tank.

The superheated AN slurry is sent to Spherodizer B301 by means of Slurry Pump P201.

The residence time in the slurry tank is adjusted in such a way that possible CN formation is controlled.

Granulation and drying

The granulation and drying processes are achieved in the spherodizer B301.

The slurry is injected by specific sprayers receiving the slurry and hot compressed air. The number and position of sprayers are defined in order to spray the slurry uniformly on the curtains of cascading solid formed by the rotation of the spherodizer. The temperature and pressure conditions of spraying are designed for insuring the optimum layering of liquid on the solid, in order that onion skin granulation is optimized.

At the inlet of the spherodizer, the Recycling Loop Conveyor M304 feeds the spherodizer with the recycled solid from the screens S301 and the Crusher B302. The granulometry and quantity of recycled product are controlled by the operation of the Crusher and recycling of on-size product, in order to achieve the control of the size growth inside the spherodizer.

Thermal balance is then fine tuned by the flow rate of air through the Spherodizer by means of the Scrubber Outlet Blower K501.

Recycling loop

The Spherodizer Outlet Conveyor M301 discharges to the Outlet Recycling Loop Elevator M302 which transports the granules to the Product Screens S301.

On the upper mesh of the screens, the oversize granules are separated and fall directly into the Crusher B302. The broken oversize granules drop to the Recycling Loop Conveyor M304. The on-size product grade granule stream is split in two parts: the required production output goes to the product cooler feeding conveyor M303 which feeds the product cooler H401, whereas the excess flow is returned to the recycling loop conveyor M304.

Product cooling and coating

The on-size product feeds the Product Cooler H401. At the outlet of the cooler, the cold product is transferred to the Coating Drum via the Cooler Outlet Conveyor M401 and the elevator M402.

In the Coating Drum B401, the product is coated with a liquid coating agent, before being sent to the storage outside battery limits.

Gas scrubbing

The off-gases leaving the Spherodizer B301 are first sent to the Spherodizer Cyclones S302 and then directed to the Scrubber S501.

The Scrubber S501 treats the off gases from the Spherodizer Cyclones and exhaust vents coming of the Slurry Tank T203.

In the scrubber, the gases are washed by an acidic solution, in order to eliminate the remaining dusts and to neutralise the ammonia. The Scrubber Circulation Pumps P501 recycle the acidic solution which has been collected in the Scrubber Tank T501.

The solution in the Scrubber Tank T501 is maintained under pH control by injection of nitric acid. Deconcentration offtake of the washing solution is sent to the dissolving tank T203 under flow rate control and the level in the tank is controlled by addition of demineralised water or process condensate coming from the AN solution synthesis plant.

Dedusting System

A comprehensive plant dedusting system is provided to ensure a clean working environment.

A centrally located Dedusting System is provided to recover the dust from the equipment dedusting points. The major part of dust emitting locations in the process such as conveyor transfer points, elevator discharges, screens and crusher etc are connected to the dedusting system by a series of ducts which terminate at a specific Dedusting Filter S502. Each dedusting point is maintained at a slightly negative pressure by the action of the Dedusting Fan K503 which draws the contaminated air through the Dedusting Filter S502. The recovered dust is returned to the Dissolving Tank T203. In order to prevent clogging of dust recovery at the dedusting points, each of these vents is fed with hot air coming from the Hot Air Fan K502 and Dedusting Air Heater E502.

Collect of solid waste

The granulation plant must be kept out of humidity and in hot atmosphere: for this purpose, the presence of liquid inside the building is avoided as far as possible and building is maintained closed and heated. Consequently, the major part of solid waste coming from leakages or cleaning of handling equipment are recovered as solid and fully recycled inside the process.

A small remaining part which could remain on the ground floor can be transferred to the Pit T502 and recycled as liquid solution to the Scrubber Tank under flow control.

 

Ammonium nitrate HICAP granulation
Ammonium nitrate based fertilizers granulation
Ammonium nitrate HICAP granulation
Ammonium nitrate based fertilizers granulation