Solid Fertilizers

It is the original slurry granulation process, based on the use of a conventional preneutralizer reactor (PN) to neutralize phosphoric / sulphuric / nitric acids with ammonia, using the obtained slurry to manufacture granular DAP / MAP / NPKs in a rotary granulator drum, after mixing with the required quantity of other raw materials, like ammonia, potash, filler, micronutrients…Obtained product is dryed, screened, cooled and conditioned before getting the required portion of final product. This process is used both in the phosphates and nitrogenous routes, including TSP and nitrophosphates production, provided the required phosphate rock grinding, feeding, mixing and reaction facilities are supplemented. The process operates at recycle vs production ratio from 4-5:1 for NPKs till 6-9:1 for DAP / TSP, being production rate limited by the water balance. INCRO has optimized this process, including a specially designed preneutralizing system ( PN + PN pump + PN agitator ), with lower retention time and better agitation, which improves ammonia reaction efficiency, reducing its losses, increases soluble P2O5 and allows operating with lower moisture slurries, reducing recycle ratios to 3-4:1 for NPKs, 4.5:1 for DAP and 6-7:1 for TSP.

INCRO’s Pipe Reactor was the key development of fertilizer industry on the 80’s, as the capability of this equipment to handle slurries with a very low water content eliminated the water balance limitation, resulting on a considerable 30-50% recycle decrease and the subsequent production increase, mainly for NPKs with high solubility. Other high energy grades, like DAP or NPKs with a lot of sulphuric acid, also benefited from PR, but still showed some heat limitations, reducing recycle improvement to 10-30%. Further INCRO’s developments along these years resulted in different PR versions, with improved reaction efficiency and versatility to operate at different conditions, with different acids and at different production rates. Presently INCRO has more than 10 different PR designs, built on different materials of construction, operating with different acids (phosphoric acid, sulphuric acid, nitric acid, or a combination of two of them), accepting liquid or gas ammonia feeding and designed for various capacities, from 10 to 120 tph of different grades, like DAP, MAP, NPKs or ammonium nitrate.

Main Pipe Reactor advantages are:

• Low moisture slurries, resulting on lower recycle ratio and higher production rate
• Low energy consumption, mainly fuel for drying and power for conveying equipment
• Lower maintenance costs
• Smaller investment
• Better product quality, mainly moisture, hardness and nutrients solubility
• Flexibility of settings compared with PN
• Great adaptability for revamps

This is a unique process, only licensed by INCRO, based on the combined use of an optimized PN along with 1 or 2 PRs, all of them simultaneously feeding slurries to granulator, with the rest of the plant having a similar arrangement to PN or PR alone units.

INCRO’s mixed system gets the advantage of both systems, avoiding water or heat limitations, thanks to heat split in two reaction systems, providing at the same time the flexibility to operate with different production schemes ( PN, PR or PN+PR ) depending on manufactured grade and available raw materials, getting always the lowest recycle ratio (2-3:1 for NPKs, 3.5-4:1 for DAP). It is the preferred system for DAP large plants and several sulphuric-phosphoric acid based NPKs.

Main Mixed Process advantages are:

• Versatility of the installation to manufacture practically all granulated fertilizer grades (PN, PR or PN+PR).
• Best compromise between water and heat balances, resulting on lower recycle for DAP and some NPKs.
• Reduction of shutdown time, as two reactions systems are available.
• Total flexibility of the settings in combined operation.
• Better control of granules shape.

The large number of plants designed by INCRO allow us to have the expertise to continuously improve the design of the screening, dedusting and scrubbing systems, being perfectly adapted to all foreseen fertilizer grades.

This is an improved version of conventional steam granulation processes, where solid raw materials and intermediate products are granulated using steam and small quantities of water. INCRO incorporates different additional granulating agents, like sulphuric acid and ammonia (direct feeding or through a special PR), or urea / ammonium nitrate solutions, both providing additional heat, thus improving final product quality. These plants, typical of complexes without phosphoric acid, do not have enough reaction heat, making difficult the recovery of the water employed in the scrubbing system. INCRO has carried out extensive research to modify granulation systems to reduce handled gas volumes, including gas recycling and minimizing scrubbing liquid volumes, till achieving zero liquid effluents, similarly to the slurry processes.

Besides TSP granulation with reactor slurry process, INCRO also has technology for powder SSP and TSP manufacturing by Kuhlmann belt process. Finely grinded phosphate rock and phosphoric or sulphuric acid, for TSP and SSP respectively, are dosed and mixed in a small reactor, with the reaction being completed in a large long residence time belt. Obtained powdery product is cured in the storage for some days-weeks, before being granulated with steam, at very low recycle rates (1-1.5:1), in a typical solids granulation plant.

INCRO has developed and patented two different processes to manufacture ammonium nitrate solution 80-97%, using 52-60% nitric acid and ammonia, one of them using Pipe Reactor (PR) and the other using a Multitubular Reactor (MTR). Both processes are highly efficient, very ecological and steam self-sufficient for required concentration, being suitable, not only for fertilizers production, but also for explosives. Process characteristics are furtherly detailed in the explosive section.

Obtained solution can be directly dispatched as final product, or employed as one of the required raw materials for manufacture of calcium ammonium nitrate (CAN) / ammonium sulphonitrate (ASN) granulation, or to be concentrated till 99.5-99.8% for pure ammonium nitrate / calcium ammonium nitrate prills production.

Before prilling, ammonium nitrate solution 95-97% is concentrated to 99.5-99.8%, which is the required concentration for any fertilizer prilling grade. AN 34.5% N is the direct product resulting from solution prilling, whereas CAN grades 33.5% N and 26-27% N are obtained mixing the concentrated AN solution with finely grinded dolomite. Different additives can be previously mixed to enhance product quality, prilling conditions…Obtained product is screened, cooled and conditioned before storage. INCRO has paid a lot of attention and research on reducing prilling tower gases impact, designing patented recycling and washing systems.

The ammonium nitrate solution obtained in the reaction section (96-97% AN) can be directly fed to a granulation unit, adding finely grinded dolomite in case of CAN manufacture, or crystal ammonium sulphate for ASN production, conducting granulation in a pug-mill, or a granulator drum, using a similar scheme to the one described for solids granulation process. In this case, compared with prilling tower, handled gas volumes are considerably reduced, saving on plant investment in that particular area and obtained granules are larger than prills, but on the other hand recycle ratios are larger and product is not so spherical.

INCRO also developed processes for some special products, like crystal MAP, double salt Ammonium sulphonitrate (ASN) and Calcium Nitrate (CaN).

Crystal MAP is a pure high grade totally soluble product (typically 12-61-0), to be used in gardening, greenhouses and drop irrigation. It is manufactured by reaction of purified / clarified phosphoric acid with ammonia, followed by filtration, evaporation and crystallization.

Ammonium sulphonitrate is a unique process, developed by INCRO’s mother company FERTIBERIA, simultaneously reacting nitric acid, sulphuric acid and ammonia. Final ASN product has double salt structure, instead of ammonium nitrate / ammonium sulphate salts mixing, resulting on higher quality, namely increased solubility and hardness.

On the nitrates line, INCRO also has technology and operating plant for soluble calcium nitrate, a valuable product used in fine fertilization. Finely grinded limestone is reacted with nitric acid and resulted solution is ammoniated, filtered and concentrated, before being granulated in a pug-mill or rotary granulation drum. The plants is equipped with high efficiency scrubbing systems.