Compost granulation method

Details Compost granulation method Compost granulation method

2000-05-05

2003-06-24

Lechert, Jr., Stephen J. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Forming articles by uniting randomly associated particles

Agitating to form larger particles

C264S128000, C071S064020, C071S064050, C071S064060

Reexamination Certificate

active

06582637

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to granulation of compost materials and more particularly, the present invention relates to a method of producing high quality granulated compost and multiple component compost granules for fertilizer applications.
BACKGROUND OF THE INVENTION
The granulation art is a mature art and recently significant advances have been made by Derdall et al., U.S. Pat. No. 5,460,765, issued Oct. 24, 1995 and subsequently by Phinney in U.S. Pat. No. 6,013,209, issued Jan. 11, 2000.
With reference to Derdall et al., this disclosure provided teachings which advanced this art by demonstrating that an ultra fine powder (−200 mesh) does not cause nucleation of the powder, but rather results in adhesion of the material to large round pellets. This process is not unlike the proverbial growth of a snowball. The technique invented by Derdall et al. clearly provides excellent process control needed to effectively maximize the contact of fine particles with binder. As a result, binder additions of 5% and less are routinely used where the previous art required approximately double this amount. As is evident, if the amount of binder can be reduced, the amount of feedstock in the particle can be increased, which, in turn, provides an improved pellet or granule.
The Derdall et al. process established that a large significant crystal or seed is critical to perform the granule formulation in one step. Although this is a significant advance in the art, it does not contemplate granulation of materials directly on the pan. If a mixture of material which contains the feedstock to be granulated and moisture is provided in a pre-moistened mixture, there is effectively no seed or nucleating agent present. This material is then used directly on the pan containing the powdered feedstock to facilitate growth of a granule.
Derdall et al. advanced the granulation art significantly by demonstrating that powdered material could be granulated, provided a seed material was used as an initiator to grow the particle. Prior to the efforts by Applicant, Derdall et al. effectively taught the state-of-the-art and is an extremely useful process when seed material can be used to form a granule. Such granules have obvious cores in the center of the granule.
In the art, it has been generally recognized that any particle greater than +150 mesh and −100 mesh causes over-nucleation on the pan which inevitably leads to the particles sticking together in agglomerated groups. This led to the conclusion that in order to make a strong enough pellet a binder must be present in an amount generally between 4% to 10% in order to effect proper adhesion of the materials into a consolidated particle.
The Derdall et al. reference clearly teaches that there are stability problems with the process if one uses a seed which exceeds certain size parameters. In summary, Derdall et al. was the first to provide a process for granulating powdered material.
Turning to the Phinney disclosure, an advance over what was initially demonstrated in Derdall et al., was provided. In the Phinney patent, it was found that if one were to use a nucleating agent, which is effectively a powder in the size range of −35 mesh to 150 mesh, a seed could be grown and composed of the same material of the final product in a size distribution of approximately −8 mesh to +4 mesh. The distinction between Derdall et al. and the Phinney patent resides in the fact that Phinney recognized that a seed was not initially required to effect granulation; the seed could be formulated by using an initial nucleating material in a powder form to first formulate a seed which could be later grown in further granulation operations. This resulted in significant advantages in terms of the final product quality. One of the chief advantages is directed to particle strength and uniform material accretion about the seed. In view of the fact that the nucleating material used was effectively infinitesimally small, the Phinney granules effectively had no core relative to the particles produced by the Derdall et al. method. In this manner, the particles produced according to the Phinney methodology provide particles having a uniformed and uninterrupted cross-section. Accordingly, a higher feedstock content could be included in each granule or pellet.
The Phinney and Derdall et al. references have provided significant instruction in the granulation art with respect to materials having fairly high bulk density. In the case of these references, sulfur has been illustrated as an example that could be granulated. Sulfur has a fairly high bulk density, approximately of the order of between 30 and 35 pounds per cubic foot (lbft-
3
). This bulk density presents a particle size of between about 180 mesh and 300 mesh. At this bulk density, there is sufficient mass to permit the granulation of the product. It has been found that this is not the case with all materials and problems can arise when the bulk density drops from the value indicated for sulfur to, for example, compost. The granulation of compost material presents unusual complications. Compost material, when pulverized, is extremely lightweight, hydrophobic and the individual particles repel one another by electrostatic interaction. The bulk density of compost is approximately between 20 lbft-
3
to about 25 lbft-
3
, which corresponds to a particle size of generally between about 240 mesh to about 400 mesh. This powder level, taken together with the properties of compost, the techniques established in the prior art and particularly, the Derdall et al. and Phinney references, require modification under certain circumstances to effect granulation of this valuable agronomic compound.
The proposition of granulating compost has been proposed in the prior art as has the concept of coating or otherwise encapsulating seeds for the protection of the seed until such time that it is desired for this to germinate.
Typical of the prior art in this area includes the process set forth in U.S. Pat. No. 3,905,796, issued September 1975, to Ghelfi. The disclosure teaches a process for dehydrating manure based fertilizers where a homogenous and durable pulp is granulated and dried.
U.S. Pat. No. 4,082,532, issued to Imhof, Apr. 4, 1978, discloses a process for manufacturing extruded cattle manure pellets where the cattle manure is mixed into a pulp and contains a moisture content between 50 to 55% by weight. The material is extruded to form strands which are subsequently further broken down into smaller forms. In this reference and the above-mentioned reference, there is no discussion as to the use of further agricultural additives to the compost and very few details concerning the granulation. It has been discovered in the instant application that once the compost material has been dried and pulverized, it is difficult to wet this material in the absence of a surfactant. The references discussed thus far do not touch on this issue whatsoever and only provide generic teachings with respect to the granulation.
Davis, in U.S. Pat. No. 5,043,007, provides a process for the production of fertilizer or the fertilizer is binder free fertilizer. The disclosure provides for a seed material and a primary and secondary nutrient sources which are put into a blender under heat until the slurry is formed. The slurry is transferred to a dryer and the product dried under vacuum and thereafter cooled to produce a granular or semi-granular fertilizer with a core of a seed material and a coating of a secondary nutrient crystallized thereabout.
In U.S. Pat. No. 5,725,630, issued to Roberts et al., Mar. 10, 1998, a fertilizer plant is set forth as well as a dry granular fertilizer. The granular fertilizer contains a C1-C6 alkanoic acid or salt of this-compound added on to a dry carrier form of granular fertilizer. This is a simple coating process and does not provide a granule having ancillary or auxiliary fertilizer compounds granulated uniformly therein.
Turning to additional prior art in the fertilizer/seed en

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