EP0416018A1

EP0416018A1 - Controlled release fertilizer

Info

Publication number: EP0416018A1
Application number: EP89906673A
Authority: EP
Inventors: Robert Peng Kwan Leet
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-05-25
Filing date: 1989-05-19
Publication date: 1991-03-13
Also published as: WO1989011462A1; EP0416018A4; MY111146A

Abstract

Un procédé de préparation de fertilisant se présentant sous forme de pastilles, de granulés ou d'agglomérats, consiste à appliquer une matière ou un mélange nutritif organique de matières nutritives organiques naturelles ayant des propriétés de liaison, de scellement ou d'enrobage à l'égard d'un fertilisant ou d'un mélange de fertilisants inorganiques organiques, avec ou sans agents améliorant le sol; et/ou à enrober d'un fertilisant en pastilles, granulés ou agglomérats, soit d'une seule substance nutritive soit de substances nutritives multiples, soit organiques ou inorganiques soit un mélange des deux, avec ou sans oligo-éléments, agents améliorant le sol, pesticides ou régulateurs de croissance, ou agents favorisant la croissance, ou soufre élémentaire, ou matières inertes.A method for preparing fertilizer in the form of pellets, granules or agglomerates, consists in applying an organic nutritive material or mixture of natural organic nutritive materials having binding, sealing or coating properties to the regard to a fertilizer or a mixture of organic inorganic fertilizers, with or without soil improvers; and / or to coat with a fertilizer in pellets, granules or agglomerates, either of a single nutritive substance or of multiple nutritive substances, either organic or inorganic or a mixture of the two, with or without trace elements, agents improving the soil , pesticides or growth regulators, or growth promoting agents, or elemental sulfur, or inert materials.

Description

CONTROLLED RELEASE FERTILIZER This invention relates to fertilizers and refers particularly, though not exclusively, to slow or controlled release fertilizers. Controlled release fertilizers are throughout this specification referred to as "CRF".

Considerable research and investigation has taken place in attempts to develop or treat conventional fertilizer materials to overcome the significant problem of fertilizer losses, and the associated problems of environmental pollution. Additional research and development has taken place in attempts to reduce the costs of the materials, the cost of production or processing of the fertilizer, the handling and application, and to increase the fertilizer efficiency by providing fertilizer materials with controlled or slow release properties. .Amongst the wide range of products and technologies that have been developed there is the method of coating of conventional fertilizers with a physical barrier such as, for example, sulphur, synthetic organic materials, or resins are included. However, because of the various inherent disadvantages and limitations these have met with very limited commercial success and the use of these has been quite slow and mainly restricted to ornamental horticulture within specified environments, and certain specialty crops.

The initial rate of nutrient release from most known CRFs coated with synthetic organic or resin products, and in particular those coated with sulphur, ranges from nil, very low, to lower than the average rate of release of the product. Thus, in several situations, particularly in low temperatures, the CRFs do not adequately synchronise nutrient availability with the physiological needs of the plant.

Consequently, these CRFs have been found to be inferior in performance than a number of applications of the appropriate conventional fertilizers, which are substantially cheaper. For example, sulphur-coated DAP has been tried and reported by TVA to give inferior performance to untreated DAP. On the other hand, most of the uncoated slow release organic fertilizers and one known inorganic NPK fertilizer known under the trade mark "Nitrophoska" and which consists of water- soluble and water-insoluble nutrients in compact pellets, have little in the way of controlled release of the water-soluble nutrients requiring considerable care in application rates so as to avoid any damage to the plants concerned.

Known sulphur-coated CRFs have been noted for their erratic performance as their nutrient release rate is subject to the oxidation of the sulphur by the soil micro-organisms and, to a lesser extent, to changes in temperature. The nutrient release rate of known synthetic organic coated CRFs, such as, for example, "Nutricote", is highly influenced by temperatures, limiting their application to controlled environments.

Known inorganic synthetically coated CRFs provide only a limited range of raw materials, and thus lack the variety of forms as well as the variety in nutrient release characteristics which are critical for optimum plant growth and performance. To complete the full coverage for fertilizers, supplementary feeding is necessary, particularly in relation to trace elements. This is particularly noticeable with soil-less potting mixes. These devices normally control nutrient release through only one mechanism, which can be hazardous to plants if it fails. For example, if the coating ruptures due to exposure to high temperature. Such CRFs lack the flexibility to adapt to the wider needs or requirements. Known sulphur coated CRFs require a high sulphur content in the range of 16% to 20% by weight as well as reinforcement with hydrophobic materials ranging from 1.7% to 2.1%, and in many cases 2.5%, conditioners, to control nutrient release for specialty applications. Continuing the applications of these CRFs in soils which are acidic and/or on plants which are sensitive to acidic conditions, further aggravates the problem. Known CRFs with sulphur or other synthetic coatings require all of the nutrient to be water-soluble and of high purity. Sources of such nutrients are substantially more costly than conventional inorganic, organic and mineral fertilizers, and are subject to chemical interactions in certain situations. For example, water-soluble phosphates interact with copper salts to form cupric phosphate which is relatively unavailable. These water-soluble inorganic materials do not contribute to the healthy development of a full range of soil micro-organisms, nor do they improve the physical structure of the soil. For those who believe in and advocate the use of micro-biologically active fertilizers, this constitutes a serious problem for their adoption. The use of up to 15% of the gross weight of fertilizer of inert and synthetic coatings which do not have any nutrient value is another disadvantage with these CRFs. Known inorganic CRFs play no role in assisting the recycling of the abundant amount of organic waste or bi-products, an increasing need in most developed countries. Being essentially synthetic in origin, the capital investments and the high energy requirement in the manufacture and/or processing make the cost of these inorganic CRFs beyond the reach of the general agricultural sector, except for some involving specialty crops. The main disadvantages of organic slow-release fertilizers are their low nutrient content, not being in the ratio for optimum plant growth and performance, and, in certain situations, the significant imbalance in nutrient content can be detrimental or even damaging to the plants. For example, pelletized poultry manure contains a relatively high quantity of phosphorus which can be injurious to phosphorus-sensitive plants of the Proteaceae family. Uncoated organic pellets are not stable and release the water-soluble nutrients, particularly nitrogen and, in some cases, organic acids, in excessive amounts immediately on application. This can be very hazardous to plants. Some organics require sterilization to prevent the spread of disease through the soil and into the plants.

The present invention attempt to overcome these problems and short-comings of the known CRFs as described above. The invention provides the means to sterilize and economically recycle organic waste and bi-products as well as water weeds and algae by the use of chemical fertilizers, preferably of high nutrient content, as carriers. The invention identifies and provides means to treat the appropriate natural organics, which have excellent plant nutrition values, and are biologically active, into binding, sealing, and fertilizer coating agents (hereinafter referred to as "BCOs"). It also provides the means and process to bind, mix, pelletize or granulate, seal and coat fertilizer materials with the BCOs, preferably with reinforcement by elemental sulphur to form a substantially firm, durable, water-insoluble, and to some extent water-impermeable coating to control nutrient release closely in line with the physiological needs of the plants. Equally importantly, it attempts to promote and nourish the very wide range of soil micro-organisms and to improve the soil structure and physical conditions. The fertilizing materials being coated, or granulated or pelletized followed with coating with a BCO, may be natural organics, chemicals, and minerals, or mixture of any or all of these, in the required ratios. Pre-formed granules or pellets may be coated with BCOs as a binding agent for the granules or pellets to carry additional fertilizers, such as trace elements or elemental sulphur, with the option of being from substantial controlled release properties to limited controlled properties. Likewise, the BCO may be used to assist pelletization or granulization with controlled release properties, or with limited controlled release properties. It has been found that the following organic materials are suitable for use as binding, sealing and coating agents:

(a) animal and fish bi-products containing collagen, preferably with protein and fat, such as, for example, meat and bone meal, blood and bone meal;

(b) collagen extracts with or without other protein and fat;

(c) seaweed, and algae. The algae acts mainly as a sealing agent; and

(d) vegetative bi-products with high protein content, such as, for example, soya bean meal acting mainly as a coating agent with minimal binding properties. These organic products are best used together in the required ratios as they reinforce each other and provide a wider range of nutrients to the plant and soil micro-organisms. These organic materials are preferably finely ground and digested before use, particularly the soya bean meal. The addition of hot water to the organics followed by gentle heating and stirring and, preferably, the addition of alkaline nutrient material, such as, for example, wood ash and lime, will give a gelatinous slurry ready for use. Other plant nutrients, organics or inorganics, such as, for example, urea or trace elements, and elemental sulphur, may be incorporated into the slurry as required. Ammonium nitrate and potassium nitrate can be incorporated into the CRF through the slurry, thereby permitting use of the full range of nitrogenous fertilizers. The use of such nitrogenous materials with elemental sulphur has previously constituted a serious fire hazard.

The warm slurry may be mixed with fertilizer materials before pelletization or granulization, or applied and mixed with fertilizer materials during granulation. Alternatively, it may be applied to preformed pellets or granules or agglomerates. Preferably, it is followed by the application of fine fertilizer material, such as, for example, organics and minerals, including those from the BCO category. More than one BCO coating alternating with fine fertilizer materials may be applied as required.

Elemental sulphur, preferably fine grade with a diameter below the range of 1 mm to 2 mm, depending on the grades of CRF being produced, is applied after coating with BCO, or BCO followed by fine fertilizer materials. This is preferably done with fine organics or minerals, such as gypsum. Fine elemental sulphur may be incorporated into the BCO to provide more body, and to reduce dust and to prevent fire hazards in situations where large amounts of sulphur are needed to be incorporated into the fertilizer as a coating. By incorporating poorly-combustible, low carbon additives, such as, for example, animal bi-products, seaweed, or well decomposed organics with elemental sulphur, it is possible to substantially overcome the hazards previously associated with the coating of granular superphosphate with large quantities of elemental sulphur in a heat melting system.

Generally only 3% to 5% of elemental sulphur i^s adequate to reinforce the BCO coating. This can be further reduced if required where significant amounts of trace elements, for example 2.5% zinc sulphate, are incorporated into the BCO coating. Hydrophobic materials may be employed as one of several means to reinforce the final coating.

Depending on the grade of the CRF being produced and the dehydration facilities or systems available, the BCO coated pellets or granular fertilizer is either: (a) dehydrated followed by heat melting the coating; or

(b) the coating is heat melted partially or fully before dehydration; or

(c) partially heat melted, followed by heat dehydration and finally heat melted to the required intensity; or

(d) dehydration without heat melting the coating where only limited controlled release features are required. Where required, coating (s) may be applied following dehydration with or without heat melting as either liquid(s), oils, molten sulphur, or fine solids and either as fertilizers, pesticides, innoculum, plant growth regulators, colouring, or hydrophobic sealants. The flexibility of the process of the present invention lends itself for incorporation either midstream or down-stream in existing fertilizer products plants for application when and as required. Therefore, for a relatively low capital outlay, significant savings in handling in the processing cost for CRF products can be achieved. A number of examples will now be described by way of non-limitative example only and for exemplifieation. EXAMPLE 1: Production Process "Seed" fertilizers in the form of dry or moist solids, which may be chemical components, a chemical-organic fertilizer mixture, or a chemical-organic-mineral fertilizer mixture is introduced into a rotating pan with burners directing the flame onto the fertilizer so as to maintain a warm temperature in the range of 50° to 75°C. Other means of generating heat, such as ammonia/acid reaction, may be employed if desired.

A slurry fertilizer (BCO), prepared by mixing in water at warm temperature (60° to 80°C, preferably 65°C) with constant stirring of an organic fertilizer such as blood and bone, with any of the following as examples - seaweed, molasses, soya bean meal paste, fish meal, compost, well rotted manure, and optionally also containing inorganic fertilizers, is formed into a gelatinous slurry containing sufficient water to ensure free-flowing conditions at warm temperatures. The total water input is in the range of 10% to 12% depending on the grades being processed. The slurry fertilizer is added in calibrated quantities to the "seed" fertilizers and mixed with special apparatus which form the second aspect of the invention so as to cause granulation and coating of the "seed" fertilizers. The granules may then be further developed into the required size and composition by the addition of finely ground organic fertilizer. Calibrated quantities of elemental fine sulphur, or preferably a mixture of sulphur with organic fertilizers or gypsum, are added to provide the final coating to the granules.

The granules are then conveyed to the rotary dryer where the moisture is reduced to around 1.5%.

As the granules reach the discharge end of the rotary dryer, the sulphur and organic coating (with the additives) is heat melted by burners firing directly onto the granules to form a firm, durable and substantially water-insoluble complex. Fat, which is present in the blood and bone, assists the water impermeability of the coating. The granules are then passed to a vibrating sieve to separate the granules as they cool down so that those excessively fine are recycled. The granules are allowed to cool gradually in bins and then packed ready for use.

EXAMPLE 2 - Organic-Sulphur Coated Complete CRF

Raw Material Percentage by Weight

Meat and bone meal, collagen extracts 8 . 0

Seaweed 0 . 5

Other organic nutrient materials 35 . 5

Ammonium nitrate (33%N) 5 . 0 Diammonium Phosphate (18/20) 10 . 0

Monoammonium Phosphate (12/22) 10 . 0

Ground Rock Phosphate (15%P) 2 . 5

Potassium Sulphate (40%K) 15 . 0 Magnesium Sulphate (9%Mg) 3 . 5 Elemental Sulphur - fine (less than 2 mm) 7 . 5

Gypsum (CaSO₄) 2 . 5

Total: 100 . 0%

Granule Size: 2-7 mm

This complete horticultural CRF has been designed to supply nutrients for more than three months under outdoor conditions and longer under indoor conditions, for both soil-less potting mixes and ground application. The very wide range of plant nutrient materials being employed for this product is to provide a wide range of nutrient types and to provide for a variety of nutrient release rates, particularly in phosphates for efficient uptake by the plant and minimal fixation by the soil. The dissolution rate under continuous wetting on fine sand is 15% after one week and 22% after this second week, then gradually at less than 0.5% per day. This dissolution rate has been found ideal for plant growth and performance. Extensive pot and field trails on various potting media indicate that it gave earlier plant responses and supports more rapid and distinctly healthier plant growth of young plants, hardier and better quality foliage and blooms than known complete CRFs such as, for example, sulphur, the synthetic organics, and synthetic resin coated products at equal product rates. The micro-biologically active features of the coating of this example could be readily observed. The product does not need more than normal watering, as is the case with the CRF with the other forms of coatings, nor supplementary nutrient feeding.

EXAMPLE 3 - Organic-Sulphur Coated Phosphatic Fertilizer

Raw Materials Percentage by Weight Triple Superphosphate (TSP) 20.5%P; 1.5%S 85.0

Elemental Sulphur - fine to less than 1mm diameter 8.5

Meat and bone meal 3.0

Seaweed/compost 0.5 Gypsum - fine, dry 2.5

Urea 0.3

Wood Ash 0.2

Total: 100 . 0%

Granule Size: 1-5 mm This CRF grade has been designed for efficient processing in the standard TSP plant with sulphur supplements, at a minimum additional processing cost as well as a means to reduce the amount of Fines in the recycle, thereby increasing the out-put of the plant. By employing a BCO with alkaline reactions, it substantially neutralises the free acid as well as the initially very acidic mono-calcium phosphate reaction product in the TSP fertilizer thereby indirectly reducing the rate of release of the fertilizer phosphate and fixation by the soil, as well as reducing any harm to the soil micro-organisms, or damage to seeds.

Field trials on natural pasture have indicated that the product according to these examples stay intact and last longer than seven months when top dressed. Pot trials using top soil/fine sand mix (to form a loamy soil) indicate that natural pasture develops and grows significantly better than Single Superphosphate (SSP), and conventional TSP. Pot trials on various vegetables indicate that this product is distinctly superior to conventional TSP and SSP. One pot trial with top soil/sand mix on Chinese spinach, for example, gave the following yield results on the 37th day:

Fertilizer Treatment Rate/Pot (g) Yield (fresh wt.) /Plant (σ)

SSP 10 0.205

TSP 5 0.261 Product of this Example 5 0.350

Control - 0.173

This product keeps and blends well with other fertilizers, including urea, providing the scope for significant cost savings in comparison with TSP or SSP-Sulphate of Ammonia mixtures. If sulphur is not required as a supplement, it can be partially substituted by organic by-products and/or magnesium or nitrogenous fertilizers resulting in further savings as well as an agronomically better product. EXAMPLE 4 - Organic-Sulphur Coated MAP

Raw Material Percentage by Weight

Monoammonium Phosphate (MAP) 12%N; 22%P 40.0

Ground Rock Phosphate - 15.5%P 30.0 Gypsum 4.5

Natural Organics - Compost 10.0

Seaweed 0.5

Blood & Bone and Collagen Extract 10.0

Elemental Sulphur - Fine 5.0

Total: 100.0%

Granule Size: 2-6 mm

On pot trials using fine sand/saw-dust mix on maize showed seed germination and development was significantly superior after treatment with the product of this example than the standard MAP, at equal product rates. Pot trials using top-soil/fine sand mixes on Chinese spinach, cabbage, pumpkin, maize and natural pasture indicated that at half the product rate of SSP, and at equal rates to DSP, TSP, the product of this example significantly supports better growth of the plant.

A further pasture trial indicated that the products of this example, when top dressed, last longer than eight months, with roots developing around some of the granules some months after application, indicating an ideal phosphorus uptake situation.

A major advantage of the product of this example is the very significant reduction in the material cost of the product compared with the standard MAP or substantially improving its efficiency through the controlled release mechanism, and the provision of a wider range of plant nutrients, particularly the mineral and trace elements from natural sources.

Up until now there has been no known method or mechanism for the processing of fertilizer products in a rotating pan involving the use of highly sticky, gelatinous binding and coating organic agents which are not readily quick-setting. Small quantities of starch has been known to be used to assist in the binding of ground-rock phosphate/elemental sulphur mixtures, and has been used with granular fertilizers to assist in the coating of a small quantity of elemental sulphur so as to provide firmer granules, but not to any extent that is water insoluble, nor have any nutrient controlled release properties.

The pan assembly of the current invention provides means to mix, granulate, coat, cool and dehydrate fertilizer products effectively with a minimal Fines or oversize granules needing to be recycled. It has a wide ranging capability to handle highly gelatinous binding, sealing and coating agents. The pan assembly of the current invention provides a safe means to heat melt the elemental sulphur coating effectively, providing an alternative to the molten sulphur spray system used previously.

The pan assembly comprises a generally circular pan having an upright rim, said pan being able to rotate about a centrally substantially vertical axis, and being provided with:

(a) a mixer-disperser unit comprising a first plurality of downwardly-extending curved tines of approximately equal length, disposed in a generally upright and evenly-spaced array on a first tine holder means which ii approximately parallel to, and spaced apart from, the pan so that the tines nearly touch the pan, and which is supported on a shaft means extending outwardly above the rim of the pan, said tine holder means being rotatable about the shaft means; (b) an oversize-breaker/discharge unit comprising a second plurality of tines and second tine holder means which are as defined above, but wherein said second tines and said second tine holder are shorter than those of the mixer-disperser unit, and (c) cleaner means to prevent accumulation of coated product on the surface of the pan, said oversize breaker/discharge unit being positioned so that product meets same before meeting the mixer-disperser unit. Preferably the mixer-disperser unit and the oversized breaker/discharge unit are provided with locking means so that it may be locked either upright ("full on"), parallel to the pan ("full off"), or at any position therebetween. Preferably the length of the tine holder means of the mixer-disperser unit is approximately 1/3 to 1/2 the diameter of the pan, more preferably 1/3 of said diameter.

The tines may be oriented so that their tips lie in a substantially straight line, or with alternate tines curving in opposite directions so that their tips lie in two substantially straight lines.

Preferably the tine holder means is a hollow cylinder or pipe which is mounted on a solid cylindrical shaft of smaller diameter. Preferably the shaft is fixed firmly above the rim of the pan, and extends outwardly beyond the rim.

The position of the tines may be controlled either automatically or manually; the latter is preferably used only for small or medium size pans (up to 8 feet diameter). Either or both of manual and automatic controls may be present, and either may be used as suitable in particular circumstances. Hydraulic control is a particularly useful form of automatic control. Preferably the tines of the oversize breaker/discharge unit reach only half way from the first tine holder means to the surface of the pan. A clearance of 30 mm is most preferred for use with fertilizer products. Preferably the overall length of the tine holder means of the oversize breaker/discharge unit is approximately 1/4 to 1/3 of the diameter of the pan, more preferably approximately 1/4.

The height of the oversize-breaker/discharge unit above the pan is adjustable, so that it can be moved into or out of the path of the granules.

The oversize-breaker/discharge unit is engaged near the end of the process, in order to break up or scoop out oversize granules. Automatic cleaning means for the pan are required if sticky or gelatinous products are to be mixed. Suitable cleaning means include scrapers running parallel to the surface of the pan from its centre of the rim, and upright from the surface of the pan parallel to and to the top of the rim, respectively. It is essential in these circumstances that the surface of the pan be provided with cleaning means; such means for the rim are optional.

Preferably the scrapers are reciprocating scrapers. These may be operated manually or automatically.

Reflector means may optionally be provided at the rim of the pan to direct product granules away from the rim and thus prevent over-concentration of product at the periphery of the pan. Preferably the reflector means is placed about 1/4 of the circumference of the pan from the mixer/dispersion unit. More preferably the reflector means is adjustable, depending on the speed of rotation of the pan, the load and the size and bulk density of the product granules. Means for application of direct heat, for example gas burners, may be used to keep the coating slurry liquid, to accelerate the coating and granulation processes, and to enhance evenness of coating and granulation. Heat also accelerates chemical interaction between the coating slurry and the dry fertilizer, and in solidifying, hardening and drying of the coated granules.

If direct heating with gas burners is used in the coating of fertilizer products with sulphur, a flame guard should be placed between the rim and the flame, in order to prevent sticky material from drying on to the rim with possible consequential burning of the product. The flame guard also serves to reflect heat back to the fertilizer in the pan. In use, the second tine holder means is preferably initially engaged in the 1/4 - 1/2 on position to assist the mixer/disperser unit to break up oversized granules, to reduce or prevent any tendency to form oversized granules during the granulation or coating stage of the process, and to discharge any unbreakable oversized granules before they grow larger. The tines can be adjusted downwards to assist in the discharge of fully granulated and coated particles when desired. It will be readily appreciated by those skilled in the art that it is possible to use two of the pans according to the invention in a continuous process, or alternatively, a 'double' or 'triple deck' rotating pan with two or three levels of surfaces respectively may be employed. The mixer/disperser unit, and the oversize breaker/discharge unit for the lower pan surface can then be extended accordingly, as exemplified by the drawing of the mixer/disperser unit in Figure 3.

Once the coating has been completed, the coated granules are discharged to a dryer means, which may for example be a rotary dryer, or a rotary drum which incorporates a heat-melt section.

The combination of mixer-disperser unit and oversize breaker/discharge unit according to the invention enables the production of firmly granulated, uniformly coated granules, with minimum production of oversize granules and fines. This enables maximum utilization of energy, and increases the rate of production. Although the apparatus according to the invention is described in relation to fertilizer production, it will be readily apparent to those skilled in the art that the apparatus is suitable for use in the mixing, granulation and coating of any product involving a sticky or densely gelatinous material, and thus is applicable in fields other than fertilizers, such as food, pharmaceutical and mineral processing. The apparatus is suitable for drying granules or for increasing the size of granules. Such applications are clearly understood to be within the scope of the invention.

Figure 1 shows the construction of a preferred embodiment of the pan granulation and coating apparatus of this invention. A flat circular pan (1) with an approximately vertical rim (2) rotates about an approximately vertical axis at its centre. The arrow indicates the direction of rotation. A mixer-disperser unit (3) comprises curved tines (4) arrayed on a cylindrical tine holder (5) supported on a cylindrical shaft (6) which extends outwardly over the rim (2).

An oversize-breaker/discharge unit (7) is constructed similarly to the mixer-disperser unit (3) having tines (8), a tine holder (9) and a shaft (10). However, the oversized-breaker/discharge unit (7) is shorter than the mixer-disperser unit (3), and its tines are held at a greater height above the pan.

Both of these units are rotatable about their shafts (6) and (10) respectively, so that the tines (4) and (8) can be adjusted relative to the pan (1). Preferably both units may also be moved horizontally, to and fro between the rim (2) and the centre of the pan (1).

A reflector (11) adjacent the rim (2) directs product granules towards the centre of the pan (1), preventing them from accumulating at the periphery. A flame guard (12) is supported from above so that it shields the rim (2) from the heat supplied by gas burners (13) supported on a horizontal shaft (14) lying over a diameter of the pan (1). The flame guard prevents sticky material from drying on the rim (2). It is necessary to provide burners (13) only at one location, although an additional set could be useful for particular applications.

A reciprocating scraper (15) travels along the horizontal shaft (14) and a second reciprocating scraper (16) travels along a vertical shaft (17) adjacent the rim (2). These scrapers (15) and (16) prevent the sticky or gelatinous product from building up on the surface of the pan (1) and rim (2). Both scrapers may be operated either manually or automatically. The shafts (14) and (17) on which the scrapers are mounted are preferably rotatable. It is preferred that scraper (15) and burners (13) be mounted on a single shaft (14), since such a construction is more compact. The shaft (14) may comprise a cylindrical external housing which carries the burners (13), having a central rotatable rod which carries the reciprocating scraper (15) (construction not shown).

In use, the coating solution is sprayed into the pan 1 from overhead sprays (18).

The pan (1) is supported by legs (19). The size and spacing of the tines (4) and (8) of the mixer-disperser unit (3) and the oversizebreaker/discharge unit (7) will depend on the product to be mixed, in particular on the difficulty of granulation, and the size and degree of compaction of granules required. These units may suitably be provided with interchangeable tine holders (5) and (9), providing different sets of tines (4) and (8) for different circumstances.

Figure 2 shows in greater detail a particularly preferred embodiment of the mixer-disperser unit (3). For use with fertilizer, the tines

(4) are suitably 30 to 35 mm apart. The tine holder

(5) is attached to an F-shaped holder (20) which carries a shaft (21) connected to a hydraulic control means (not shown), and a second shaft (22) and handle (23) for manual operation. Holes (24) and (25) in the shafts (21) and (22) for manual and hydraulic operation respectively enable the unit to be locked with a locking pin (not shown) into the "full off" position. A further set of holes (26) enables the unit to be

Saimilarly locked into range of "on" positions, up to "full on". Similar details of construction are applicable to the oversize breaker-discharge unit (7). Neither the mixer-disperser unit (3) nor the oversize breaker/discharge unit (7) need be oriented along a diameter of the pan (1). Both of these units may be at any desired angle to a diameter, depending on the degree of mixing required. The units are supported on their respective shafts (6) and (10) from outside the pan (1), so that their angle and distance from the rim (2) may be adjusted as required. Although it is clear that more than one of units (3) and/or (7) may be provided, I have found that one of each results in adequate mixing of fertilizer products, and that more than one of either unit may cause excessive turbulence or friction. However, this will depend on the product to be mixed.

The mixer-disperser unit (3) is placed in "full on" position during the start of the process, when the "seed" fertilizer is introduced into the pan (1). Its role is to disperse, as well as to prevent the unwanted over-agglomeration of the fertilizer particles or granules after the solution has been introduced, at the same time assisting in the turning and mixing of the fertilizer particles, and assisting a more uniform coating of the granules to the required size. The adequately-coated granules float up over the smaller-sized finer granules, and it is the function of the set of tines (4) to retain these and not allow them to rotate around the pan for further coating and in competition with the incompletely granulated or coated fertilizer. This allows the final application of coating agents, such as elemental sulphur, to be directed on these "retained" granules.

The oversize breaker/discharge unit exerts a strong force on large granules trapped by its tines. The weaker granules break and the resultant fragments are forced through the tines. The harder granules are retained by the tines, and build up until they spill over the edge of the pan. This unit can act as a scoop in the "full on" position, in which most of the larger granules are trapped.

Under the batch production system the set of tines (4) is partially rotated "full up" off the fertilizer to allow for the fully-coated granules to rotate around the pan (1) for consolidation, hardening and partial drying by the direct flame from the burners (13). The set of tines is engaged to the "full on" position again for the discharge of these granules. Some process routes of the invention are fairly well illustrated in Figure 4 of the drawings in which the following explanation can be given to each of the numbered boxes.

1A FERTILIZER MATERIALS

Organics, Minerals, Chemicals, TE. Granular, or fine or mix of both.

2A COATING PREFORMED GRANULES WITH BCO. 3A PELLITIZATION.

4A MIXING WITH BCO1.

5A COATING WITH BCO.

6A EXTRUSION INTO SPIKES.

7A PELLITIZATION. 8A COATING WITH FINE ORGANICS, MINERALS.

9A COATING WITH BCO².

10A COATING WITH S + ORGANICS ETC.

11A COATING WITH S.

12A COATING WITH ORGANICS, MINERALS, NO SULPHUR. 13A COATING WITH TE.

14A SIEVE OUT OVER-SIZED PELLETS/GRANULES.

15A OVERSIZE GRANULES/PELLETS TO CHAIN MILL/PUG-MILL.

15A1 DEHYDRATION & HEAT MELTING OF COATING

DEHYDRATION - HEAT MELT DEHYDRATION - NO HEAT MELT

HEAT MELT - DEHYDRATION HEAT MELT - DEHYDRATION - HEAT MELT

20A SECONDARY COATING

AS LIQUIDS AS SOLIDS

AS MOLTEN SULPHUR

23A SCREENING

24A COOLING

25A BAGGING 26A BULK

27A BLENDING WITH OTHER FERTILIZER(S)

28A FINES RECYCLE

29A DIRECT TO FIELD

Claims

The claims defining the invention are as follows:

1. A process for preparing fertilizer in pellet, granular or agglomerate form comprising:

(a) applying

(i) a natural organic nutrient material or (ii) a mixture of natural organic nutrient materials which has binding, sealing and coating properties and preferably elemental sulphur to a fertilizer or a mixture of organic inorganic fertilizers, with or without soil conditioner (s) ; and/or

(b) coating a pelletized, granular or agglomerate fertilizer, either of single nutrient or multiple nutrients, either organic, or inorganic or a mixture of these, with or without trace elements, soil conditioner (s) , pesticides or growth regulators, or growth promoters, or elemental sulphur, or inert materials .

2. A process claimed in claim 1, wherein there is included subsequent heating of the pellets, granules, or agglomerate fertilizer formed to a temperature above the melting point of the sulphur, and preferably to melt both the elemental and natural organic nutrient material to form a firm, durable, substantially water-insoluble and to some extent water impermeable coat matrix, either at a uniform or intermittent temperatures.

3. A process as claimed in claim 1 or claim 2, wherein there is included further applying fine solid(s) or a mixture of these, or liquid (s) or molten sulphur, either as fertilizer(s), or soil conditioner(s) or as sealant(s), or pesticide (s) , or growth regulator(s), or inert material (s), to provide colouring, either uniformly or intermittently.

4. A process as claimed in any one of claims 1 to 3, in which the natural organic nutrient binding, sealing and coating materials are used to form pellets, granules, and agglomerates.

5. A process as claimed in any one of claims 1 to 4, in which the binding, sealing, and coating materials are selected from the group comprising:

(i) animal and fish by-products which contain collagen; (ii) animal and fish by-products which contain fat; (iii) animal and fish by-products which contain protein; (iv) seaweeds; (v) algae;

(vi) protein of vegetable origin; and (vii) collagen extracts, with or without fats.

6. A process as clamed in any one of claims 1 to 4, wherein the preformed pellets, granules, or agglomerates are coated with a mixture of elemental sulphur, trace elements and organic fertilizers including any of or a mixture of these materials as claimed in any one of claim 5, inorganic fertilizers and soil conditioners.

7. A fertilizer in pellet, granular, or agglomerate form produced by the method of any one of claims 1 to 6.

8. A rotating pan assembly consisting of a mixer-disperser unit; an oversize-breaker/discharge unit to provide means to mix, granulate, coat, heat melt, dry or cool fertilizer materials, human food, pharmaceutical products, industrial materials, pesticides, growth promoters and regulators, and any other suitable products.

9. A coating apparatus for coating a granular product, said apparatus comprising a generally circular pan having an upright rim. said pan being able to rotate about a central substantially vertical axis, and being provided with:

(a) a mixer-disperser unit comprising a first plurality of downwardly-extending curved tines of approximately equal length, disposed in a generally upright and evenly-spaced array on a first tine holder means which is approximately parallel to, and spaced apart from, the pan so that the tines nearly touch the pan, and which is supported on a shaft means extending outwardly above the rim of the pan, said tine holder means being rotatable about the shaft means; (b) an oversize-breaker/discharge unit comprising a second plurality of tines and second tine holder means which are as defined above, but wherein said second tines and said second tine holder are shorter than those of the mixer-disperser unit, and said oversize breaker/discharge unit being positioned so that product meets same before meeting the mixer-disperser unit.

10 Apparatus as claimed in claim 9, where said mixer-disperser unit and said oversized- breaker/discharge unit are provided with locking means so that it may be locked either upright, parallel to the pan, or any position therebetween.

11. Apparatus as claimed in claim 9 or claim 10, herein the length of the tine holder means of the mixer-disperser unit is approximately 1/3 to 1/2 of the diameter of the pan.

12. Apparatus as claimed in any one of claims 9 to 11, wherein the tines are oriented so that their tips lie in a substantially straight line.

13 Apparatus as claimed in any one of claims 9 to 12, wherein the tines are oriented so that the tips of alternate tines curve in opposite directions so that their tips lie in two substantially straight line.s.

14. Apparatus as clamed in any one of claims 9 to 13, wherein the tine holder means is a hollow cylinder or pipe which is mounted on a solid cylindrical shaft of smaller diameter, said shaft being fixed firmly above the rim of the pan and extending outwardly beyond the rim.

15. Apparatus for the coating of granular products substantially as hereinbefore described with reference to the accompanying drawings.