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

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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.


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


Coogee / Australia

in operation


2004 Pilot unit, Rotoform PCS / Tennessee USA

in operation

Fertilizerurea / technicalurea


Coromandel / India

in operation


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

underconstruction

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&grinding 200MTPD

AzomuresRomania underconstruction

NPK with ingredients for fertilizer

2011 2 Rotoforms 240 MTPD + down stream

SABIC Al Bayroni / KSA

underconstruction 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



Technology

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