Full paper gives how Rotoform process can meet the expectations of enhansed fertilizersizers. Deatilled scheme and process is explained. A case story is also explained based on the recent order from Zaklady Azotowe Pulawy S.A
Technical paper on Enhansed fertilizers U+AS and U+S Page 103 116 Sandvik - swamy & nanz & roth
- 103 -Producing UAS and US enhancedfertilizersRealizing a win-win situation foreverybodyKUMAR SWAMY, ULRICH NANZ, B. ROTHSandvik Process SystemsFellbach, GermanyThe United Nations Environment Program (UNEP) has acknowledged the contribution offertilizers in improving food security. At the same time, it has also called for efficient use of thefertilizers. High nitrogen and phosphorus inputs have enabled high crop yields from land thatwould otherwise have low productivity. It is however necessary to enhance the input ofnutrients to soils and achieve these high yields in a sustainable fashion.Integrated nutrient management ensures that the right fertilizers are applied in the rightdose 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 ofsulphur is now limiting further crop yields while also reducing nitrogen application efficiencies.Fertilizers containing nitrogen and sulphur are enhanced fertilizers, which increase crop yieldsand 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 flexibleand environmentally friendly way.INTRODUCTIONThe United Nations Environment Program (UNEP) has acknowledged the contribution of fertilizers inimproving food security. At the same time, it has also called for efficient use of the fertilizers. High nitrogenand phosphorus inputs have enabled high crop yields from land that would otherwise have lowproductivity. It is however necessary to enhance the input of nutrients to soils and achieve these highyields in a sustainable fashion.
K. Swamy, U. Nanz, B. Roth104 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 maximizecrop 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 limitingfurther crop yields while also reducing nitrogen application efficiencies. Fertilizers containing nitrogen andsulphur are enhanced fertilizers, which increase crop yields and nitrogen application efficiencies, realizinga 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 andenvironmentally friendly way.CURRENT CROP NUTRIENT SITUATIONLaw of minimumThere is a growing realization that crops need more nutrients than just nitrogen (N). Other primarymacronutrients 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 themicronutrients: boron (B), copper (Cu), iron(Fe), manganese (Mn), zinc (Zn), chloride (Cl), nickel (Ni), andmolybdenum (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 limitgrowthLow nitrogen application efficiencyThe most commonly applied nitrogen fertilizers are urea and ammonium nitrate. In general, nitrogenapplication efficiencies are very low as between 30 and 50% of the nitrogen supplied to the soil is typicallylost to air and water, causing more and more environmental problems. In Canada, for example, urea hasbecome 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 surfaceapplications of urea is that the N is susceptible to ammonia volatilization. The urea molecule, in thepresence of moisture and the soil enzyme urease, converts to ammonium carbonate, which can lead to theproduction of ammonia gas.
Producing UAS and US enhanced fertilizersNitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013) 105Fig. 2: Typically between 30 and 50% of the urea applied is lost to air and waterSulphur is fourth plant nutrientSulphur 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 tablebelow.Table 1Nutrient requirements of selected crops, kg/haN P K SRice 150 25 150 20Wheat 168 34 110 25Corn 360 52 230 50Soybean 200 25 110 15Rapeseed 90 16 110 35Cotton 140 37 85 20Oil palm 193 36 249 75Tea 290 130 65 45Source: The Sulphur InstituteThis recognition of the role of sulphur is taking place at a time when evidence is mounting of an increasingsulphur deficiency in soils throughout the world.There are several reasons for this:High analysis N, P and K fertilizersIn the continuing quest for increasing yields, the use of high-analysis NPK fertilizers has occurred at theexpense of other, sulphur-based fertilizers. Fertilizer manufacturers have long endeavoured to eliminatenon-nutrient elements from fertilizers in order to economize on transport and distribution costs. Productdevelopment on maximizing the N, P and K content of fertilizers has resulted in the virtual elimination of Sexcept where it was added intentionally.One of the primary sources of sulphur was ammonium sulphate (21-0-0-24S), but during the 1960s manyfertilizer 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 beenwidely 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 bechemically produced, while KCl can be extracted from natural ores by flotation.
K. Swamy, U. Nanz, B. Roth106 Nitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013)Increasing crop yieldsIncreasing crop yields are removing greater amounts of S from the soil. Over the past 40 years, nitrogenconsumption has increased at a much higher rate than that of sulphur consumption. The increasedconsumption 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 asubstantial sulphur fertilizer deficit, which was at that time between 2-2.5 million tons in Asia. This deficitwas 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 provincescollected over 8,000 soil samples to determine plant-available S levels. It was estimated that 27% of thesamples from the southern Chinese provinces and 52% of the samples from the north-eastern provinceswere deficient in S for the growth of most crops.Lower sulphur emissionsSulphur emissions from industrial plants are declining, mainly as a result of tougher environmentalstandards worldwide.One can state that sulphur deficiency has become a problem in all parts of the world. The Sulphur Institutehas estimated that sulphur deficiency amounts to 600,000 tons in Western Europe and up to 10.5 milliontons 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 Sfertilizers that are well distributed by surface broadcasting and are subject to granule decomposition canoxidize to plant-available S forms. This oxidation is performed by naturally occurring soil bacteria andfungi.However, the rate of this biological oxidation process is difficult to predict, leading to similar difficulty inpredicting the required fertilizer S rate. Achieving the desired distribution and application lead-time for S0oxidation becomes more difficult in direct seeding systems, where the plant nutrients are applied in a bandat the time of seeding. When S0 sources are applied in confined band or seed row applications, the rate ofoxidation may be too slow to maximize crop uptake.Particle size is therefore an important determinant of the effectiveness of elemental S. In warm zones, aparticle size of less than 250 mu is necessary for nearly all the elemental S to be oxidized and thusbecome plant-available in the year of application. Smaller particles are necessary for equal performance inother regions.Sulphur with bentonite seems to be a nice technical solution to produce small particle sulphur. Sulphur ismixed with 10% bentonite which, in contact with water, swells up and creates small particles sulphur. Thiskind of fertilizer has been produced for more than 25 years using Sandvik Process Systems’ Rotoformgranulation 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 aby- or co-product of caprolactam production. Japan, Russia and the United States are leading suppliers ofthis 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 severalothers routes such as coke ovens, as a by-product of methyl methacrylate, direct synthesis from ammoniaand sulphuric acid, from sulphur rich tail gas treated with ammonia, and as a by-product of nickel leaching.
Producing UAS and US enhanced fertilizersNitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013) 107WHY 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 ofwhich many participate in the vital functions of the plants.Sulphur plays an important role in plant growth. It is an essential amino acidcomponent and is active in important biochemical and physiologicalprocesses including lipid and protein biosynthesis, photosynthesis, Nassimilation, N biological fixation, and others (Mengel&Kirkby, 2000; Rice,2007). The connection between N and Sis thus strong at the cellular andwhole plant level.The graphic on the right side illustrates the importance of ensuringsufficient nitrogen and sulphur nutrients together.As the graphic shows, crop yields resulting from the application of 140kg/ha N are similar to – or even less than – those achieved when nonitrogen or sulphur fertilizer is used.By adding sulphur, the crop yield can be increased significantly.Imbalances in plant nutrition of nitrogen and sulphur inhibit theeffective function of nitrogen and reduce the nitrogen applicationefficiency: valuable plant nutrient is lost into either the soil or theatmosphere, causing environmental concerns. This is also clearlyillustrated in the figure above. Adding 140 kg/ha nitrogen withoutrealizing a higher crop yield: One can imagine that a significantamount 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, whichin turn results in lower ammonia volatilization.From a farmers point of view, the most economic and convenient method of applying additional plantnutrients is likely to be as an ingredient of his regular fertilizer treatment. To this extent, numerousadvances have been made in formulating materials and developing innovative technologies for addingsulphur to fertilizers.HOW TO PRODUCE UAS AND US?Two technologies have been developed for the production of UAS with a significant amount of AS: fluidbed granulation and the Sandvik Process Systems Rotoform.Fluid bed granulationYara 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 some500 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 SPicture 3: Effect oflow sulphur levelInfluence of S-fertilizer on Yieldof winter raps (1990 test resultsin Bayern Germany)
K. Swamy, U. Nanz, B. Roth108 Nitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013)• The presence of ammonium sulphate crystals in the injected feedstock results in a slightly differentproduct build-up, where some internal seeding influences the seed balance in such a way that lessoversize crushing is required without sacrificing the product size flexibility.• The end product needs to be coated with a proprietary liquid agent to avoid further moistureuptake during bulk storage and handling in wet climatic conditions.The addition of ammonium sulphate to urea provides an overall improvement in the physico-chemicalproperties of granules compared with urea, as can be seen in the table below.Table 2Product quality comparison: UAS granules vs Urea granules (Yara fluid bedgranulation)UAS granules Urea granulesMoisture 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 kgAverage size between 2.0 and 3.5 mmBulk density loose 780-800 g/l 730-750 g/lBulk density tamped 820-840 g/l 770-790 g/lCoating liquid 1% noneSandvik Process Systems’ RotoformThe 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 identicalRotoform lines. Furthermore, the S content can be varied across a significant wider range than with thefluid 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
Producing UAS and US enhanced fertilizersNitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013) 109The feed to the Rotoform is urea melt with a concentration of 99.6 wt%; in existing urea plants this can bebranched 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 (HighSpeed) drop former, patented by Sandvik, consists of a heated stator and a perforated rotating shell thatturns concentrically around the stator to deposit drops of urea across the full width of the belt. Thecircumferential speed of the Rotoform is synchronized with the speed of the steel belt cooler ensuring thatthe drops are deposited on the belt without deformation and, after solidification, results in regular pastilleswith an optimum shape.Fig. 6: Rotating shell deliversdroplets of the required sizePicture 7A/B: Urea pastilles on the steel cooling beltThe rotating shell contains rows of small holes, which are sized to deliver the required product size. Theheat released during crystallization and cooling is transferred by the stainless steel belt to the coolingwater. 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 offormaldehyde. The size of the Rotoform product is same as for granules, and this size can easily be variedbetween 1 and 5 mm. Pastilles are extremely uniform, more so than granules, and additional screening isnot required. The shape and form of the Rotoform product has been shown to be extremely popular withfarmers.
K. Swamy, U. Nanz, B. Roth110 Nitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013)After solidification the pastilles are smoothly released from the steel belt via an oscillating scraper. Theproduct then falls directly onto a conveyor belt for transfer to storage. The section above the moving steelbelt is enclosed with a hood and vented.There are no large airflows involved in this technology and no visible urea dust emission. What ammoniavapours are produced can easily be captured in a simple atmospheric absorber; this results in negligibleemissions of ammonia and urea, a unique feature of this technology.Picture 8: Rotoform High Speed
Producing UAS and US enhanced fertilizersNitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013) 111Picture 9: Rotoform lines operating in parallelTo produce UAS with a Sandvik Rotoform, urea melt and solid AS are mixed and then ground in ablending 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 soonas the sulphate, leading to low biuret contents. The ammonium ion in ammonium sulphate displaces theequilibrium of the dimerization of urea to biuret, so that no further increase in biuret concentration is notedas soon as both components are mixed as a solution/slurry. We expect that UAS produced with theSandvik Rotoform technology will have a lower biuret content than pure, and that UAS with significantlyhigher levels of AS can be produced.UAS is no exception to the rule that mixed salts are more hygroscopic than their components. Therefore, acoating will be necessary as the critical relative humidity of UAS is about 40% at 20°C.Fig. 10: Flow scheme to produce UAS
K. Swamy, U. Nanz, B. Roth112 Nitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013)Picture 11: Blending unit to produce urea/ASA single Rotoform line has a typical capacity of 120-150 mtpd depending on the choice of the variant. Thecapacity of UAS would be same.The introduction of specialty urea products can be realized smoothly as producers can begin with a singleRotoform line, which can be brought into and out of production whenever required. When market demandincreases, 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 theRotoform. 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 idealstorage behaviour (no caking).Another process option is to use solid sulphur and dose the sulphur with the mixer grinder (similar to theproduction of UAS).After the pastilles have been distributed onto the soil, bacteria will transform the elementary sulphurparticles into sulphate. Because of the insolubility of elementary sulphur in water, this fertilizer isconsidered a slow release product with high anti-caking behaviour.Sandvik’s Rotoform granulation technology offers the ideal solution of the production of EnhancedFertilizers like UAS and US.Picture 12A/B: UAS and US Enhanced Fertilizer productsMajor advantages of this approach include the flexibility to adjust the AS or S content to the specific cropneeds, and the ability to adjust production to meet market demand.
Producing UAS and US enhanced fertilizersNitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013) 113Sandvik’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 densityIn addition, UAS and US products present the opportunity for producers to achieve higher profit margins byupgrading low value AS and S to higher value products.OTHER NUTRIENT ADDITIONSIt is possible to produce a wide range of specialty urea products – in addition to fertilizer grade urea – withSandvik’s Rotoform granulation technologyThe 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• SulphurbentonitePlease find below the reference list of the Rotoform technology for urea and fertilizer products
K. Swamy, U. Nanz, B. Roth114 Nitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013)Table 3Rotoformer reference listYEARPLANTCAPACITYCOMPANY/LOCATIONSTATUS PRODUCT/APPLICATION20001 Rotoform120 MTPDESSECO /ItalyinoperationSulphurbentonite/ fertilizer20021 Rotoform120 MTPDCoogee /AustraliainoperationSulphurbentonite/ fertilizer2004 Pilot unit, RotoformPCS / TennesseeUSAinoperationFertilizerurea /technicalurea20051 Rotoform120 MTPDCoromandel /IndiainoperationSulphurbentonite/ fertilizer20065 Rotoforms300 MTPDPCS /Georgia USAinoperationTechnical grade urea2006till20094 Rotoforms240 MTPDZlotniki /PolandinoperationMg-N + CaN/fertilizer2008Pilot productionunit125MTPDYARA. / Brunsb.GermanyPilotProductionUrea +10%S;fertilizerurea;YEAR PLANT CAPACITYCOMPANY/LOCATIONSTATUS PRODUCT/APPLICATION20081 Rotoformunit 120MTPDACRON /VelikiyNovgorod /RussiainoperationTechnical andfertilizerurea20101 Pilot Rotoformunit + dosing +mixing & grindingPetrobrasSergipe / BrazilunderconstructionUrea+additives for urea based fertilizers2010Rotoform unit +mixing andgrinding200 MTPDAzomuresRomaniaunderconstructionAmmonium nitrate with ingredientsfor fertilizer2010Rotoformunit +dosing&mixing&grinding200MTPDAzomuresRomaniaunderconstructionNPK with ingredientsfor fertilizer20112 Rotoforms240 MTPD + downstreamSABICAl Bayroni / KSAunderconstructionTechnical grade urea
Producing UAS and US enhanced fertilizersNitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013) 115The production process of these specialty urea products is fairly simple and straightforward. In some casesone simply injects a liquid additive into the urea melt; in other cases a blending unit is applied to grind andmix the solid additives into the urea melt.The pictures below show various specialty urea products.Picture 13: Various specialty fertilizer products produced with Sandvik RotoformCONCLUSIONS• 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 beproduced by the Sandvik Rotoform pastillation process.• Producing UAS and US leads to a Win-Win situation for everybody: Higher profit margins for theproducer, higher crop yields to the farmer and less environmental concerns for all of us.Notes:Agrium Fertilizer Facts, Spring 2003Granular urea-ammonium sulphate, A new fluid bed granulation product, V. Bizzotto, NSM Netherlands, (TA/84/7)Richard Hands, BCInsight, Fertilizer Focus November/December 2012
K. Swamy, U. Nanz, B. Roth116 Nitrogen + Syngas 2013 International Conference (Berlin, Germany 5-8 March 2013)