Technical paper on Enhansed fertilizers U+AS and U+S Page 103 116 Sandvik - swamy & nanz & roth

- 103 -
Producing UAS and US enhanced
fertilizers
Realizing a win-win situation for
everybody
KUMAR SWAMY, ULRICH NANZ, B. ROTH
Sandvik Process Systems
Fellbach, Germany
The United Nations Environment Program (UNEP) has acknowledged the contribution of
fertilizers in improving food security. At the same time, it has also called for efficient use of the
fertilizers. High nitrogen and phosphorus inputs have enabled high crop yields from land that
would otherwise have low productivity. It is however necessary to enhance the input of
nutrients to soils and achieve these high yields in a sustainable fashion.
Integrated nutrient management ensures that the right fertilizers are applied in the right
dose to maximize crop production, avoid loss of nutrients and meet environmental concerns.
Until now, the emphasis has been on the use of NPKs but a worldwide deficiency of
sulphur is now limiting further crop yields while also reducing nitrogen application efficiencies.
Fertilizers containing nitrogen and sulphur are enhanced fertilizers, which increase crop yields
and nitrogen application efficiencies, realizing a win-win situation for everybody: the farmers,
the fertilizer producer and the environment.
This paper describes how these enhanced fertilizers can be produced in a very flexible
and environmentally friendly way.
INTRODUCTION
The United Nations Environment Program (UNEP) has acknowledged the contribution of fertilizers in
improving food security. At the same time, it has also called for efficient use of the fertilizers. High nitrogen
and phosphorus inputs have enabled high crop yields from land that would otherwise have low
productivity. It is however necessary to enhance the input of nutrients to soils and achieve these high
yields in a sustainable fashion.

K. Swamy, U. Nanz, B. Roth
104 Nitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013)
Integrated nutrient management ensures that the right fertilizers are applied in the right dose to maximize
crop production, avoid loss of nutrients and meet environmental concerns.
Until now, the emphasis has been on the use of NPKs buta worldwide deficiency of sulphur is now limiting
further crop yields while also reducing nitrogen application efficiencies. Fertilizers containing nitrogen and
sulphur are enhanced fertilizers, which increase crop yields and nitrogen application efficiencies, realizing
a win-win situation for everybody: the farmers, the fertilizer producer and the environment.
This paper describes how these enhanced fertilizers can be produced in a very flexible and
environmentally friendly way.
CURRENT CROP NUTRIENT SITUATION
Law of minimum
There is a growing realization that crops need more nutrients than just nitrogen (N). Other primary
macronutrients that plants need to take in are phosphates (P) and potassium (K); others – carbon (C),
oxygen (O) and hydrogen (H) – are available through air (via the photosynthesis process) and water.
Then there are the secondary macronutrients: calcium (Ca), magnesium (Mg) and sulphur (S); and the
micronutrients: boron (B), copper (Cu), iron(Fe), manganese (Mn), zinc (Zn), chloride (Cl), nickel (Ni), and
molybdenum (Mo), which are also essential for plant growth but required in much smaller quantities.
Finally, silicon (Si) and cobalt (Co) are also beneficial for some plants in even smaller quantities.
A deficiency of any single nutrient is enough to limit growth as is indicated in the pictures below.
Fig. 1A/B: A plant needs many different nutrients. A deficiency of any single nutrient is enough to limit
growth
Low nitrogen application efficiency
The most commonly applied nitrogen fertilizers are urea and ammonium nitrate. In general, nitrogen
application efficiencies are very low as between 30 and 50% of the nitrogen supplied to the soil is typically
lost to air and water, causing more and more environmental problems. In Canada, for example, urea has
become the broadcast fertilizer of choice for many winter wheat growers on the Canadian Prairies,
especially since ammonia nitrate fertilizer was removed from the market. The problem though with surface
applications of urea is that the N is susceptible to ammonia volatilization. The urea molecule, in the
presence of moisture and the soil enzyme urease, converts to ammonium carbonate, which can lead to the
production of ammonia gas.

Producing UAS and US enhanced fertilizers
Nitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013) 105
Fig. 2: Typically between 30 and 50% of the urea applied is lost to air and water
Sulphur is fourth plant nutrient
Sulphur has for too long been defined as a secondary nutrient; this under-values its importance. Belatedly,
sulphur is becoming regarded as the fourth plant nutrient – after N, Pand K – as illustrated in the table
below.
Table 1
Nutrient requirements of selected crops, kg/ha
N P K S
Rice 150 25 150 20
Wheat 168 34 110 25
Corn 360 52 230 50
Soybean 200 25 110 15
Rapeseed 90 16 110 35
Cotton 140 37 85 20
Oil palm 193 36 249 75
Tea 290 130 65 45
Source: The Sulphur Institute
This recognition of the role of sulphur is taking place at a time when evidence is mounting of an increasing
sulphur deficiency in soils throughout the world.
There are several reasons for this:
High analysis N, P and K fertilizers
In the continuing quest for increasing yields, the use of high-analysis NPK fertilizers has occurred at the
expense of other, sulphur-based fertilizers. Fertilizer manufacturers have long endeavoured to eliminate
non-nutrient elements from fertilizers in order to economize on transport and distribution costs. Product
development on maximizing the N, P and K content of fertilizers has resulted in the virtual elimination of S
except where it was added intentionally.
One of the primary sources of sulphur was ammonium sulphate (21-0-0-24S), but during the 1960s many
fertilizer manufacturers raised the N content by substituting ammonium nitrate (35% N) and urea (46% N).
Single superphosphate (0-20-0-14S) was another useful source of sulphur but this product has been
widely superseded by the higher-analysis triple superphosphate (0-48-0) and DAP (16-48-0).
Similarly, few potash producers have included sulphur in their product by chance. KCl (50-63% K2O)
contains more potassium than K2SO4 (50-54% K2O). Potassium sulphate is more expensive and must be
chemically produced, while KCl can be extracted from natural ores by flotation.

Increasing crop yields
Increasing crop yields are removing greater amounts of S from the soil. Over the past 40 years, nitrogen
consumption has increased at a much higher rate than that of sulphur consumption. The increased
consumption of S-free, high-analysis fertilizers is one of the most significant causes of S deficiency.
In 1995 The Sulphur Institute (TSI) estimated that increasing fertilizer requirements have spawned a
substantial sulphur fertilizer deficit, which was at that time between 2-2.5 million tons in Asia. This deficit
was expected to rise to 5.5-6 million tons by 2010, of which China will account for 4.1 million tons, or 45%
of the region’s entire fertilizer deficit. A survey of S-supplying status of soils in 12 Chinese provinces
collected over 8,000 soil samples to determine plant-available S levels. It was estimated that 27% of the
samples from the southern Chinese provinces and 52% of the samples from the north-eastern provinces
were deficient in S for the growth of most crops.
Lower sulphur emissions
Sulphur emissions from industrial plants are declining, mainly as a result of tougher environmental
standards worldwide.
One can state that sulphur deficiency has become a problem in all parts of the world. The Sulphur Institute
has estimated that sulphur deficiency amounts to 600,000 tons in Western Europe and up to 10.5 million
tons worldwide. And this gap is continuing to increase.
SULPHATE OR ELEMENTAL SULPHUR?
Nowadays ammonium sulphate (AS) and elemental sulphur (S0) are the two main S fertilizer sources.
While AS provides S in the plant-available sulphate form, S0 first needs to undergo oxidation. Elemental S
fertilizers that are well distributed by surface broadcasting and are subject to granule decomposition can
oxidize to plant-available S forms. This oxidation is performed by naturally occurring soil bacteria and
fungi.
However, the rate of this biological oxidation process is difficult to predict, leading to similar difficulty in
predicting the required fertilizer S rate. Achieving the desired distribution and application lead-time for S0
oxidation becomes more difficult in direct seeding systems, where the plant nutrients are applied in a band
at the time of seeding. When S0 sources are applied in confined band or seed row applications, the rate of
oxidation may be too slow to maximize crop uptake.
Particle size is therefore an important determinant of the effectiveness of elemental S. In warm zones, a
particle size of less than 250 mu is necessary for nearly all the elemental S to be oxidized and thus
become plant-available in the year of application. Smaller particles are necessary for equal performance in
other regions.
Sulphur with bentonite seems to be a nice technical solution to produce small particle sulphur. Sulphur is
mixed with 10% bentonite which, in contact with water, swells up and creates small particles sulphur. This
kind of fertilizer has been produced for more than 25 years using Sandvik Process Systems’ Rotoform
granulation technology and has proven to be a very popular fertilizer.
Both sulphur and ammonium sulphate are widely produced. Much of ammonium sulphate is produced as a
by- or co-product of caprolactam production. Japan, Russia and the United States are leading suppliers of
this relatively inexpensive product and most ammonium sulphate is produced as a fine (small particle)
crystalline material, marketed as "standard product". But ammonium sulphate is also produced via several
others routes such as coke ovens, as a by-product of methyl methacrylate, direct synthesis from ammonia
and sulphuric acid, from sulphur rich tail gas treated with ammonia, and as a by-product of nickel leaching.

WHY NITROGEN AND SULPHUR TOGETHER IN ONE FERTILIZER?
Plants take up sulphur in the form of sulphate (SO42-), and between 80-90%
of total S goes into making S-amino acids like methionin, cystin and cystein.
The rest is required for the synthesis of other S-containing compounds of
which many participate in the vital functions of the plants.
Sulphur plays an important role in plant growth. It is an essential amino acid
component and is active in important biochemical and physiological
processes including lipid and protein biosynthesis, photosynthesis, N
assimilation, N biological fixation, and others (Mengel&Kirkby, 2000; Rice,
2007). The connection between N and Sis thus strong at the cellular and
whole plant level.
The graphic on the right side illustrates the importance of ensuring
sufficient nitrogen and sulphur nutrients together.
As the graphic shows, crop yields resulting from the application of 140
kg/ha N are similar to – or even less than – those achieved when no
nitrogen or sulphur fertilizer is used.
By adding sulphur, the crop yield can be increased significantly.
Imbalances in plant nutrition of nitrogen and sulphur inhibit the
effective function of nitrogen and reduce the nitrogen application
efficiency: valuable plant nutrient is lost into either the soil or the
atmosphere, causing environmental concerns. This is also clearly
illustrated in the figure above. Adding 140 kg/ha nitrogen without
realizing a higher crop yield: One can imagine that a significant
amount of nitrogen will get lost to the environment in such a situation.
Furthermore the presence of ammonium sulphate ensures a lower soil pH than with standard urea, which
in turn results in lower ammonia volatilization.
From a farmer's point of view, the most economic and convenient method of applying additional plant
nutrients is likely to be as an ingredient of his regular fertilizer treatment. To this extent, numerous
advances have been made in formulating materials and developing innovative technologies for adding
sulphur to fertilizers.
HOW TO PRODUCE UAS AND US?
Two technologies have been developed for the production of UAS with a significant amount of AS: fluid
bed granulation and the Sandvik Process Systems Rotoform.
Fluid bed granulation
Yara and SKW Piesteritz in Germany produce UAS by means of patented fluid bed granulation technology.
However, these technologies are not licensed out, and require a minimum production capacity of some
500 mtpd and a relative high initial investment.
Key points/requirements of the Yara production process are:
• Injection of a solution/suspension of ammonium sulphate crystals into the urea melt feed.
• Clog-free header design and erosion-resistant spray-nozzle specification.
Fig. 4: The importance of N and S
Picture 3: Effect of
low sulphur level
Influence of S-fertilizer on Yield
of winter raps (1990 test results
in Bayern Germany)

• The presence of ammonium sulphate crystals in the injected feedstock results in a slightly different
product build-up, where some internal seeding influences the seed balance in such a way that less
oversize crushing is required without sacrificing the product size flexibility.
• The end product needs to be coated with a proprietary liquid agent to avoid further moisture
uptake during bulk storage and handling in wet climatic conditions.
The addition of ammonium sulphate to urea provides an overall improvement in the physico-chemical
properties of granules compared with urea, as can be seen in the table below.
Table 2
Product quality comparison: UAS granules vs Urea granules (Yara fluid bed
granulation)
UAS granules Urea granules
Moisture content 0.15 % 0.20 %
Biuret content 0.60 % 0.80 %
Total nitrogen content 41.00 % 46.00 %
Sulphur content 5.00 % -
Crushing strength (2.5 mm) 3.6 kg 3.0 kg
Average size between 2.0 and 3.5 mm
Bulk density loose 780-800 g/l 730-750 g/l
Bulk density tamped 820-840 g/l 770-790 g/l
Coating liquid 1% none
Sandvik Process Systems’ Rotoform
The Sandvik Rotoform is able to produce UAS on a smaller scale, enabling a smooth market introduction.
Based on actual market demand, additional production can be achieved by simply adding identical
Rotoform lines. Furthermore, the S content can be varied across a significant wider range than with the
fluid bed granulation, enabling the production of better customized UAS products.
The figure below shows the flow scheme of the Rotoform technology.
Fig. 5: Sandvik Rotoform granulation technology

The feed to the Rotoform is urea melt with a concentration of 99.6 wt%; in existing urea plants this can be
branched off from the urea evaporation section downstream of the urea melt pumps.
Urea is introduced under pressure (2-3 barg) in molten form to the drop former. The Rotoform HS (High
Speed) drop former, patented by Sandvik, consists of a heated stator and a perforated rotating shell that
turns concentrically around the stator to deposit drops of urea across the full width of the belt. The
circumferential speed of the Rotoform is synchronized with the speed of the steel belt cooler ensuring that
the drops are deposited on the belt without deformation and, after solidification, results in regular pastilles
with an optimum shape.
Fig. 6: Rotating shell delivers
droplets of the required size
Picture 7A/B: Urea pastilles on the steel cooling belt
The rotating shell contains rows of small holes, which are sized to deliver the required product size. The
heat released during crystallization and cooling is transferred by the stainless steel belt to the cooling
water. The cooling water is sprayed against the belt underside, absorbs the heat and is collected in pans,
cooled in a cooling system (cooling tower) and returned to the Rotoform units.
Under no circumstances can the cooling water come into contact with the urea product.
With this technology, pastilles with a high crushing strength can be produced without the use of
formaldehyde. The size of the Rotoform product is same as for granules, and this size can easily be varied
between 1 and 5 mm. Pastilles are extremely uniform, more so than granules, and additional screening is
not required. The shape and form of the Rotoform product has been shown to be extremely popular with
farmers.

After solidification the pastilles are smoothly released from the steel belt via an oscillating scraper. The
product then falls directly onto a conveyor belt for transfer to storage. The section above the moving steel
belt is enclosed with a hood and vented.
There are no large airflows involved in this technology and no visible urea dust emission. What ammonia
vapours are produced can easily be captured in a simple atmospheric absorber; this results in negligible
emissions of ammonia and urea, a unique feature of this technology.
Picture 8: Rotoform High Speed

Picture 9: Rotoform lines operating in parallel
To produce UAS with a Sandvik Rotoform, urea melt and solid AS are mixed and then ground in a
blending unit, a standard packaged unit. Up to 40wt% AS has been mixed with urea with excellent results.
With the Yara technology, when AS is added to the 96 wt% urea melt the biuret content is "frozen" as soon
as the sulphate, leading to low biuret contents. The ammonium ion in ammonium sulphate displaces the
equilibrium of the dimerization of urea to biuret, so that no further increase in biuret concentration is noted
as soon as both components are mixed as a solution/slurry. We expect that UAS produced with the
Sandvik Rotoform technology will have a lower biuret content than pure, and that UAS with significantly
higher levels of AS can be produced.
UAS is no exception to the rule that mixed salts are more hygroscopic than their components. Therefore, a
coating will be necessary as the critical relative humidity of UAS is about 40% at 20°C.
Fig. 10: Flow scheme to produce UAS

Picture 11: Blending unit to produce urea/AS
A single Rotoform line has a typical capacity of 120-150 mtpd depending on the choice of the variant. The
capacity of UAS would be same.
The introduction of specialty urea products can be realized smoothly as producers can begin with a single
Rotoform line, which can be brought into and out of production whenever required. When market demand
increases, additional lines can be installed in parallel.
Pastillation of urea with elementary sulphur (US)
The Sandvik Rotoform process can also be used to produce urea with elementary sulphur.
One method is to introduce liquid sulphur into the urea melt directly before the mixture enters the
Rotoform. A constant mixture will be achieved by exact dosing and mixing of the feeds into the system.
The formed US droplets will crystallize on the steel belt, creating very hard pastilles displaying ideal
storage behaviour (no caking).
Another process option is to use solid sulphur and dose the sulphur with the mixer grinder (similar to the
production of UAS).
After the pastilles have been distributed onto the soil, bacteria will transform the elementary sulphur
particles into sulphate. Because of the insolubility of elementary sulphur in water, this fertilizer is
considered a slow release product with high anti-caking behaviour.
Sandvik’s Rotoform granulation technology offers the ideal solution of the production of Enhanced
Fertilizers like UAS and US.
Picture 12A/B: UAS and US Enhanced Fertilizer products
Major advantages of this approach include the flexibility to adjust the AS or S content to the specific crop
needs, and the ability to adjust production to meet market demand.

Sandvik’s Rotoform granulation technology has the following features:
 High flexibility in terms of throughput/capacity
 High flexibility in product type (cooling lengths and drop formation can be accurately determined)
 Environmentally friendly technology
 Low energy consumption
 Easy to operate
 Easy to maintain
 No scale-up risks
 100% on-stream time possible
 Excellent uniformity of product
 Easy control/variation of product size
 Very low dust content
 No formaldehyde needed
 High product strength
 High bulk density
In addition, UAS and US products present the opportunity for producers to achieve higher profit margins by
upgrading low value AS and S to higher value products.
OTHER NUTRIENT ADDITIONS
It is possible to produce a wide range of specialty urea products – in addition to fertilizer grade urea – with
Sandvik’s Rotoform granulation technology
The following products have been already produced on Rotoform systems:
• Fertilizer grade urea
• Technical urea for urea-formaldehyde, melamine, ad blue production
• Urea blended with macronutrients
• Urea blended with micronutrients
• Urea with ammonium sulphate
• Ammonium nitrate
• Ammonium nitrate derivatives (KCl, Zeolite, AS < 10% and NPK)
• NPK complex fertilizer from nitrate &urea route
• Calcium nitrate
• Magnesium nitrate
• Sulphurbentonite
Please find below the reference list of the Rotoform technology for urea and fertilizer products

Table 3
Rotoformer reference list
YEAR
PLANT
CAPACITY
COMPANY/
LOCATION
STATUS PRODUCT/APPLICATION
2000
1 Rotoform
120 MTPD
ESSECO /
Italy
in
operation
Sulphur
bentonite/ fertilizer
2002
1 Rotoform
120 MTPD
Coogee /
Australia
in
operation
Sulphur
2004 Pilot unit, Rotoform
PCS / Tennessee
USA
in
operation
Fertilizerurea /
technicalurea
2005
1 Rotoform
120 MTPD
Coromandel /
India
in
operation
Sulphur
2006
5 Rotoforms
300 MTPD
PCS /
Georgia USA
in
operation
Technical grade urea
2006
till
2009
4 Rotoforms
240 MTPD
Zlotniki /
Poland
in
operation
Mg-N + CaN
/fertilizer
2008
Pilot productionunit
125MTPD
YARA. / Brunsb.
Germany
Pilot
Production
Urea +10%S;
fertilizerurea;
YEAR PLANT CAPACITY
COMPANY/
LOCATION
STATUS PRODUCT/APPLICATION
2008
1 Rotoformunit 120
MTPD
ACRON /
VelikiyNovgorod /
Russia
in
operation
Technical and
fertilizerurea
2010
1 Pilot Rotoform
unit + dosing +
mixing & grinding
Petrobras
Sergipe / Brazil
underconstructi
on
Urea+
additives for urea based fertilizers
2010
Rotoform unit +
mixing and
grinding
200 MTPD
AzomuresRomania
under
construction
Ammonium nitrate with ingredients
for fertilizer
2010
Rotoformunit +
dosing&mixing&gri
nding
200MTPD
AzomuresRomania
underconstructi
on
NPK with ingredients
for fertilizer
2011
2 Rotoforms
240 MTPD + down
stream
SABIC
Al Bayroni / KSA
underconstructi
on
Technical grade urea

The production process of these specialty urea products is fairly simple and straightforward. In some cases
one simply injects a liquid additive into the urea melt; in other cases a blending unit is applied to grind and
mix the solid additives into the urea melt.
The pictures below show various specialty urea products.
Picture 13: Various specialty fertilizer products produced with Sandvik Rotoform
CONCLUSIONS
• There is a significant worldwide sulphur deficiency, which is getting worse.
• Low sulphur levels not only limit crop yields but also decrease efficiency of nitrogen.
• Urea ammonium sulphate (UAS) and urea sulphur (US) are Enhanced Fertilizers, which can be
produced by the Sandvik Rotoform pastillation process.
• Producing UAS and US leads to a Win-Win situation for everybody: Higher profit margins for the
producer, higher crop yields to the farmer and less environmental concerns for all of us.
Notes:
Agrium Fertilizer Facts, Spring 2003
Granular urea-ammonium sulphate, A new fluid bed granulation product, V. Bizzotto, NSM Netherlands, (TA/84/7)
Richard Hands, BCInsight, Fertilizer Focus November/December 2012

Technical paper on Enhansed fertilizers U+AS and U+S Page 103 116 Sandvik - swamy & nanz & roth

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à Technical paper on Enhansed fertilizers U+AS and U+S Page 103 116 Sandvik - swamy & nanz & roth

Similaire à Technical paper on Enhansed fertilizers U+AS and U+S Page 103 116 Sandvik - swamy & nanz & roth (20)

Dernier

Dernier (20)

Technical paper on Enhansed fertilizers U+AS and U+S Page 103 116 Sandvik - swamy & nanz & roth