Calcium Ammonium Nitrate

Introduction:

Ammonium nitrate is used extensively as a nitrogenous fertilizer. It is

made exclusively by the reaction between gaseous ammonia and aqueous

nitric acid The resultant ammonium nitrate solution may be used in various

ways:-

It can be stored as a solution and then used in down-stream plants or

sold as such

It can be formed into solid ammonium nitrate by prilling or granulation

It can be mixed with solid filler. The most common filler is calcium

carbonate in the form of ground limestone, dolomite or by-product

calcium carbonate from, for example, a nitro phosphate process, to

make a product which is known in the industry as “Calcium Ammonium

Nitrate” (CAN) and then prilled or granulated. Granular products

containing ammonium nitrate and either ammonium or calcium

sulphate are also manufactured.

Gaseous ammonia may be produced on site from the vaporization of

liquid ammonia. One of the important parameters in the production of

ammonium nitrate is the strength of the nitric acid feedstock which can vary

from 50 to 70%. Normally the ammonium nitrate is made from the nitric acid

which is available from the production facility. It may also be made from

purchased nitric acid. The final solid fertilizer product may leave the

production site either as loose bulk or in a variety of pack sizes.

Characteristics:

Calcium ammonium nitrate (CAN) contain 27 % N and 20 % of ground

limestone. Nitrogen is half in the nitrate form and half in the ammonia form.

This results in rapid as well as permanent effect. The granulation of this

fertilizer ensures a quick and exact dosing. Calcium ammonium nitrate has a

form of 2 - 5 mm large of whitish till light brown color granules. The fertilizer

has excellent physical-mechanical properties and properties for storage. Bulk

density is approx. 950 - 1,000 kg.m-3 and the angle of slope is 30°.

Applications:

The applications are universal. CAN is a nitrogen fertilizer applicable

practically too all plants growths, and to all, even to more acid soils. This

fertilizer is most frequently used for maturing of cultures during vegetation.

Packing, Transport and Storage:

Like most Nitrogen products, CAN absorbs moisture from the

atmosphere. It is therefore highly recommended that it is stored either in

closed/sealed bags on pallets, or if stored in bulk, covered with a tarp. As

with most solid fertilizers, it should also be stored in a cool, dry, well

ventilated area

Calcium ammonium nitrate is delivered in bulk or on pallets per 1,200

kg (24 bags per 50 kg) fixed by a PE foil. It can be transported in railway

wagons, ships and covered road transport means. This fertilizer should be

stored according to the relevant regulations which are valid for the storage of

fertilizers.

Safety Measures:

CAN may be dangerous for human health. Avoid swallowing or

contacting with mucous membranes, eyes and repeated contact with skin.

Dust of the fertilizer is irritable and may cause over sensitiveness or eczemas.

During manipulation it is necessary to protect the skin and eyes, eating,

drinking and smoking are not allowed. After the work hands should be

washed thoroughly and regeneration cream should be used. Keep out of

reach of children and unauthorized persons.

Uses:

CAN is commonly used on fruit, process and vegetable crops.

Benefits:

Calcium Ammonium Nitrate can be considered as near-neutral in its

effect on soil pH - and therefore can be used on soils that have a low pH

without lowering further. This also means it is most suitable for using on

perennial fruit crops (where soil incorporation of lime is normally difficult to

achieve). CAN is a Nitrogen fertilizer which contains equal parts of fast acting

Nitrate-Nitrogen and longer lasting Ammonium-Nitrogen. This ensures a more

continuous nitrogen supply to the crop and thus better efficiency of use, and

also makes it suitable for unseasoned application during summer or winter.

Application (& Compatibility):

CAN may be applied in base dressings and side dressings, but the

actual rates will depend on the farm type, the region and the season. It is

most beneficial however when split applied (where possible) on a 4 - 6 weekly

basis to ensure a continuous nitrogen supply. CAN is not compatible with

Magnesium Oxide nor super phosphate. If mixed with dry lime, it may give off

ammonia gas, while mixing with Maxi Super may result in slush. Volatilization

of nitrogen from CAN is negligible; therefore the timing of the applications is

flexible.

Raw Materials:

There are two kind of raw material which are used in the production of

Calcium Ammonium Nitrate.

Calcium carbonate.

Calcium carbonate is a chemical compound with the chemical

formula CaCO3. It is a common substance found in rock in all parts of the

world, and is the main component of shells of marine

organisms, snails, pearls, and eggshells. Calcium carbonate is the active

ingredient in agricultural lime, and is usually the principal cause of hard

water. It is commonly used medicinally as a calcium supplement or as

an antacid, but excessive.

Ammonium nitrate.

The chemical compound ammonium nitrate,

the nitrate of ammonia with the chemical formulaNH4NO3, is a white

crystalline solid at room temperature and standard pressure. It is commonly

used in agriculture as a high-nitrogen fertilizer, and it has also been used as

an agent in explosives, including improvised explosive devices. It is the main

component of ANFO, a very popular explosive.

Ammonium nitrate is used in instant cold packs, as hydrating the salt is

an endothermic process. Nitric acid is typically around 60% strength; the

water in the nitric acid will be emitted from the process in one form or

another or recycled to another plant.

Production of Calcium Ammonium Nitrate:

Several proprietary processes for ammonium nitrate manufacture are

available, using various combinations of different neutralization, evaporation,

drying and finishing methods. Solid ammonium nitrate is produced in the form

of prills, crystals and granules, either alone or in combination with other

materials. Large tonnages of ammonium nitrate are also made in the form of

solutions having concentrations in the range of 80 to 90 percent, for use in

liquid fertilizers. The major unit operations used in ammonium nitrate

manufacture is described below.

The production process comprises three main unit operations:-

Neutralization

Evaporation

Solidification (prilling and granulation)

Neutralization:

The exothermic neutralization of nitric acid with ammonia gas produces

ammonium nitrate solution and steam. The nitric acid is commonly pre-heated

using equipment of suitable corrosion resistance especially if the available

concentration of nitric acid is towards the lower limit of the range 50-70%.

Pre-heating can best be performed by using steam or hot condensate from

the ammonium nitrate process.

Neutralization can be performed in a single stage or in two stages. A

two-stage neutralizer operates with a low pH in the first stage (acidic

conditions) and a neutral pH in the second stage. The equipment can operate

at a variety of operating pressures and temperatures. In most neutralizers the

pressure, temperature and concentration are linked by the boiling point

characteristics of ammonium nitrate solutions with only two of these variables

being independent.

Ammonia gas may contain small quantities of inert such as hydrogen,

nitrogen, and methane. These will be vented from the neutralizer system at a

point which depends upon the detail of the particular process.

Neutralizers:

Neutralizers may be free-boiling vessels, circulating systems, or pipe

reactors. At least 10 different types and designs of neutralizers are in use now

a day. The environmental factors which influence the choice of neutralizer

are:-

A two-stage neutralizer produces most of the boil-off steam in the first

stage and most of the ammonia emission from the second stage. This reduces

the total emission of ammonia

A single-stage neutralizer is inherently simpler and cheaper

Neutralization at an elevated pressure will produce steam at a higher

temperature (and ammonium nitrate at a higher concentration). Such steam

could be used more readily in down-stream processes such as evaporation

and drying

Whenever the operating conditions allow the addition of water to the

neutralizer, this water (for example, contaminated steam condensate) should

be used to recycle ammonium nitrate solution provided this can be performed

safely

The steam which is evolved from the neutralizer vessel contains

ammonia and ammonium nitrate in quantities to a few thousand ppm of each.

This can be reduced to a few hundred ppm by careful design of the

neutralizer

Steam purification:

The steam leaving the neutralizer can be purified, or it can be

condensed and then purified.

The steam may be used in the evaporator or it may be used to preheat and

Evaporate ammonia and it can be used to preheat the nitric acid.

The following techniques have been used commercially for the purification.

Knitted wire mesh demister pads

Wave plate separators

Fiber pad separators using, for example, fibers Scrubbing devices

Packed columns

Venturi scrubbers

Irrigated sieve plates

Ammonium nitrate emissions from neutralizers are very difficult to remove

because the particles are very fine. A combination of droplet separators and

scrubbers can be used.

Condensate treatment:

Stripping with air or steam with the addition of alkali to liberate ionized

ammonia if required

Distillation

Membrane separation processes such as reverse osmosis.

Ion exchange can also be considered but there are some safety

concerns which must be addressed. The recycle of organic resins to the

ammonium nitrate process must be prevented, and the resin must not be

allowed to become nitrated.

The choice of technique will depend on whether nitrate removal is required

and this will depend on the receiving water.

The condensate which is finally produced from the steam which leaves the

neutralizer could be discharged in one of the following ways:-

To a nitric acid plant for use as absorption water provided safety and

purity requirements of nitric acid are met

To other uses on the site such as in the manufacture of solution

fertilizers

To boiler water feed, possibly after further purification

The product from the neutralizer is ammonium nitrate solution with a

concentration which depends on the feed materials and the operating

conditions. It may be fed to storage without further processing but, if it is to

be used in the manufacture of solid ammonium nitrate, CAN, or NPK fertilizer,

it is normally concentrated by evaporation.

Evaporation:

The evaporator is normally required to remove the majority of the

water which is present in the ammonium nitrate solution Evaporation is

always performed using steam which can come from the ammonium nitrate

process (neutralizer) or from a steam raising facility on the site.

During evaporation some ammonia is lost from the ammonium nitrate solution

and this must normally be replaced prior to solidification.

Prilling and Granulation:

“Prilling” refers to the formation of granules by the solidification of

droplets of fertilizer materials. “Granulation” is a more general term and refers

to techniques using processes.

Prilling:

The feed of ammonium nitrate to a prilling plant must be substantially

anhydrous. It is formed into droplets which then fall down a tall tower (prilling

tower). Air is made to flow up the tower using fans (counter-current to the

prills) and the droplets cool and solidify.

Ground calcium carbonate (limestone or dolomite) is added prior to the

formation of the droplets when CAN is being made.

Granulation:

Some types of process equipment can be used to manufacture both

granulated AN. and CAN. Other types of equipment can be used to produce

both granulated CAN and NPK (compound) fertilizers.

Examples of granulators used in AN./CAN. plants include rotary pans and

drums, if CAN is to be produced and the ammonium nitrate is added in the

granulator as a spray of hot concentrated solution. No further drying of the

granules will normally be required. The granules are screened and the fines

and crushed oversize returned to the granulator.

Examples of CAN and CAN/NPK granulators include drums and pug

mills.

The filler may be mixed with the ammonium nitrate solution before

granulation or in the granulator itself It is important that the wet scrubbers on

a CAN plant are suitably designed to handle the inert solids without choking

and a solid waste may be produced from such scrubbers.

Cooling:

Both granulators and prills towers normally produce a product which

requires further cooling in rotary or fluid bed coolers with the air cleaned by

high efficiency cyclones, bag filters or wet scrubbers. Air cleaned in a dry

system can be generally re-used as secondary air to the drier after de-dusting

(where possible). A bulk flow heat exchanger may be used. The product is

cooled by rejecting the heat to water from a cooling tower in a development

of a plate heat exchanger.

Process Flow Sheet of Calcium Ammonium Phosphate…

Conditioning:

Ammonium nitrate and CAN are prone to caking during storage and are

conditioned to prevent caking. Ant caking agents may be internal to the

finished particle or applied as a coating to the outside. They may be of

various chemical species and are generally specified by the individual

manufacturer.

These additives may also prevent dust formation and moisture pick-up

during storage.

Physical and Chemical Properties

Appearance: White or off-white granules or prills

Odor: Odorless

PH water solution (10g/100ml) >4.5

Melting point: 160-170°C depending on moisture content

Boiling point: >210°C (decomposes by dissociation)

Explosive properties: Not explosive as per EEC test.

The fertilizer has a high resistance to detonation. This resistance is decreased

by the presence of contaminants and/or high temperatures

Oxidizing properties: Can support combustion and oxidize. Not

classified as oxidizing according to EEC

Solubility in water: 1,900g.l-1 at 20°C

Bulk density: 830 to 1,100kg/m3

Single Super Phosphate.

Phosphates Fertilizers:

Phosphate fertilizers industry is considered one of the most polluting

industries in Egypt. No modernization or pollution abatement plans and

technologies were set for this industry, in spite of the implementation of such

technologies world wide. It is worth mentioning that the production of

phosphate fertilizers in Egypt is limited (installed capacities 1.2 millions tons

15.5 P2O5) compared with nitrogenous fertilizers (installed capacities 12

million tons estimated as 15 % N2).

The various phosphate fertilizers, depending on their composition,

have different solubility in soil solutions and are, therefore, assimilated by

plants differently. Phosphate fertilizers include single super phosphate and

triple super phosphate. The single super phosphate is a mixture of mono

calcium phosphate and gypsum (available P2O5 almost 16- 22 %), while

triple-super phosphate is composed mainly of mono calcium phosphate

(available P2O5) almost 46 %).

Single super phosphate Fertilizer:

Figure presents the block flow diagram for manufacturing of Single

super phosphate fertilizers and the related raw materials and pollution

sources.

The manufacturing process depends on reacting phosphate rock with

sulfuric acid and the fertilizer contains about (16- 20 %) P2O5. The net

reaction proceeds as follows:

Ca F2. 3Ca3 (PO4)2 + 7H2SO4 + 14H2O → 3Ca(H2PO4)2 + 7Ca SO4 . 2H2O + 2HF

The process can be divided into two stages as follows:

The first stage represents the diffusion of sulfuric acid to the rock

particles accompanied by a rapid chemical reaction on the particle surface,

which continues until the acid is completely consumed, and crystallization of

calcium sulphate.

The second stage represents the diffusion of the formed phosphoric

acid into the pores of the rock particles which did not decompose. This stage

is accompanied by a second reaction.

Raw Material:

Phosphate rock:

Phosphorite, phosphate rock or rock phosphate is a non-

detritus sedimentary rock which contains high amounts of phosphate bearing

minerals. The phosphate content of phosphorite is at least 20% which is a

large enrichment over the typical sedimentary rock content of less than

0.2%.The phosphate is present as Fluor apatite typically

in cryptocrystalline masses (grain sizes < 1 μm) referred to as cellophane.

The dark brown to black beds range from a few centimeters to several meters

in thickness. The layers contain the same textures and structures as fine

grained lime stones and may represent digenetic replacements of carbonate

minerals by phosphates.

Sulfuric acid:

Sulfuric acid (sulphuric acid in British English) is a strong mineral acid with the molecular formula H2SO4. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion. Principal uses include lead-acid batteries for cars and othe vehicles, ore processing, fertilizer manufacturing, oil refining,wastewater processing, and chemical synthesis.

Production Process:

In this process ground phosphate rock is transported from the storage

site to automatic weight, by a system of belt and screw conveyors and

elevators, which feed the continuous action double conical mixer. The sulfuric

acid is continuously diluted with water in a batch mixer to a 75 %

concentration, and then fed to the mixer to react with ground phosphate rock

where a first reaction takes place. This reaction ends in the reaction mixer in

30- 60 minutes, during the period of settling and hardening of the super

phosphate slurry, which is caused by the relatively rapid crystallization of the

low solubility calcium sulphate.

The next stage of the process is ageing of the super phosphate, i.e.

the formation and crystallization of mono calcium phosphate in the den. The

formed slurry is transported to the continuous-action reaction den which has

a very low travel speed to allow for solidifying, where formation of super

phosphate takes place (settling and hardening of the slurry in the first stage

of ageing). Considerable quantities of fluoride compounds are evolved from

the acidulation, they are sent to the scrubbers.

The super phosphate powder, from the den, is transferred for ageing

by a belt conveyor, located below the den, to the pile storage for curing, or

completion of chemical reaction, which takes 2-6 weeks to a P2O5 availability

acceptable for plant nutrient. The raw fertilizer is uniformly distributed by a

scattering device and in order to accelerate the ageing operation, the super

phosphate is agitated during storage by means of a grab-bucket crane.

The end product still contains a certain amount of uncombined

phosphoric acid, which makes the fertilizer more hygroscopic. Neutralizing

admixtures are used to remove the free acid of the super phosphate, or it is

treated with gaseous ammonia. These procedures improve the physical

properties of the super phosphate. They lower the moisture content, the

hygroscopic and the tendency to cake. If ammonia treatment is used, an

additional nutritional component (N2) is also introduced into the fertilizer.

During reaction of the phosphate with sulphuric acid in the den,

hydrogen fluoride evolves and reacts with the silica contained in the

phosphates and forms gaseous silicon-tetra fluoride (SiF4) and fluo slicic acid

(H2SiF6). The continuous den is, therefore, enclosed so that fumes of these

compounds do not escape into the working place. The fluorous gases,

containing H2SiF6 vapors, are withdrawn through an opening in the den roof

into a ventilation pipe to an absorption unit and are utilized for making

sodium fluo silicates.

Super phosphate is granulated in drum granulators to improve its

physical properties. In the granulator, the super phosphate powder (after

being cured for 2-6 weeks) is wetted with water fed into the drum through

nozzles, and rolled into granules of different size which are then dried,

screened into size fractions cooled and the product is bagged in plastic

(polyethylene) bags. The over size granules are ground and recycled, with the

undersize granules, to the den.

Continuous- Action Single Super phosphate Den

(1) Rotating shell; (2) cutter; (3) partition; (4) stationary discharge pipe