EP0770151B1

EP0770151B1 - The process for mechanical treatment of woody products, the product thus obtained and its use

Info

Publication number: EP0770151B1
Application number: EP95922719A
Authority: EP
Inventors: Paolo Giampiccolo
Original assignee: KENIT Srl
Current assignee: KENIT Srl
Priority date: 1994-07-01
Filing date: 1995-06-23
Publication date: 2000-10-11
Anticipated expiration: 2015-06-23
Also published as: PT770151E; ITRM940436A0; ES2153038T3; IT1272317B; WO1996001337A1; AU2752495A; DE69519095D1; ATE196933T1; ITRM940436A1; EP0770151A1; DE69519095T2

Abstract

The process of mechanical treatment of woody parts of annual or polyannual plants covers the preparatory phases of airdried xylem fragments of textile or cellulosic plants, and to subject these fragments to mechanical pressing (3) in order to break down the macroscopic structure and to destroy vessels and medullary rays. Described are industrial plants for carrying out the process, possible shapes of the product (4) obtained and examples of the uses thereof.

Description

The present invention concerns a process for the mechanical treatment of woody products from annual or polyannual plants, as well as the product thus obtained and its use.

More in particular, the present invention concerns a process for the treatment of woody products, originating from the xylem of annual textile-fiber plants or cellulosic-fiber plants with the object to reduce the specific volume of this xylem, thus increasing the capacity and rapidity of absorption of pure liquids, solutions, emulsions, suspensions, etc., and to regulate and extend over time the release into receivers of whatever type of liquid that has been absorbed and of soluble substances possibly contained therein.

Domestication of wild-growing vegetal species for the purpose of extracting textile or cellulosic fiber, has been practised since ancient times, and has involved plants that from the taxonomical point of view belong to different families.

Fiber plants are classified according to two criteria:

A) morphological, regarding the parts of the plant from which these fibers are obtained;

B) practical, which relates to the use for which the fibers are destined which, in turn, depends on their properties.

Concerning classification "A": the class of the species relating to the present invention is that which refers to the species containing the textile fibers, or bark, on the inside of the cortical tissue of the stem. To this group belong a number of the most important textile-fiber species, such as hemp, flax, jute, ramie, kenaf, roselle, aramine, etc. These species are very often referred to as bast-fiber species and very often given the added designation of soft-fiber plants in order to distinguish them from leafy-fiber species like abaca , sisal, henequen, etc., known as hard fibers.

Concerning classification "B": this classification can refer indifferently to textile fibers, cordage fibers, textile woven and non-woven mats, fibers for making paper and fibers for other uses.

Different layers of tissue are found when sectioning the stem of this fiber species, namely:

the cuticle on which one often notices the presence of wax which functions to limit the loss of water from the stem;

the epidermis which consists of a layer of thick - walled cells containing the stomas;

the cortex which consists of two to seven cell strata;

the phloem which contains the sieve-tubes and the textile fibers that are very often grouped in bundles of varying numbers circulary positioned in the phloem parenchyma, which, once separated from the rest of the vegetable, constitute the "bark", that is to say the true and proper textile fiber;

the cambium which separates the cortical part from the internal woody core part of the stem, represented by a soft cell-stratum, having an extended, thin-walled rectangular shape;

the xylem which contains the useful material relating to the scope of the present invention and which is formed by woody cells, short and thick, that support the plant during its growth;

the pith which is situated on the inside of a cavity, located, if existing, in the centre of the stem. It consists of parenchymatous cells of minor thickness.

Xylem or woody part of the stem, has the form of a cylinder hollow in sections that decrease from the base up to the top. It varies percentage-wise in relation to the other stem components according to the species and maturity of the plant, and can range between 50% and over 70% of the stem mass. Its thickness vanes considerably from the base - where it is particularly wide and developed - to the top where it diminishes until it becomes herbaceous.

From the histological point of view, xylem normally consists of fibers that are short, relatively broad and well lignified, arranged in the direction of the axis of the stem to form a continuous cylinder crossed by medullary rays.

Inside the xylem are empty hollow formations, filled with air. These empty spaces form the volumetrically most important part of the xylem, and reduce considerably the value of the apparent density thereof. For the kenaf core (the techno-commercial denomination of kenaf xylem) such value is around 0.12 grams per cm³, whereas the real density shows values more or less in line with those woods for normal use.

Other textile-fiber plants show xylem density that is different from, and sometimes even less than that of kenaf core.

In what follows, reference is made to data relating to kenaf core, because this material is in fact preferred since considerable quantities thereof are expected to become available in the very near future.

US-A-5.316.150 discloses a method for treating herbaceous fiber producing plants in order to separate the longer outer bast fibers from the shorter woody innercore fibers.

According to the present invention, the process for mechanical treatment of woody products from annual and polyannual plants including preparing xylem fragments from textile- or cellulosic plants in dry condition is characterised by the step of subjecting said fragments to the mechanical pressing in order to provoke the breaking down of the macroscopic structure and the destructuring of the vessels and medullar rays. Now will be illustrated the structural modifications that take place in the xylem of textile-fiber or cellulosic-fiber plants when those are being subjected to dry mechanical pressing operations, resulting in high degrees of volume reductions. As well as the effect of those structural modifications on the behaviour and physical property of the material obtained.

When xylem - duly fragmented from textile-fiber or cellulosic-fiber plants with similar characteristics - is subjected to dry mechanical pressing, the fragments tend to be flattened, and the air, contained in the alveola of the original xylem structure is expelled by mechanical breakdown of the macroscopical structure of the wood. When pressure is increased, destructuring of the medullary rays and the vessels is also more or less achieved; all this with a volume decrease of 75-90% of the original volume.

In normal temperature and humidity conditions the pressed material retains the form of the mold in which it has been subjected to pressure and consequently one can have materials compressed in parallelepiped, cubic, cylindrical or whatever other desired form.

In a series of experimental tests, the press used in the experimental production produced parallelepiped briquettes (blocks) measuring 90x90x100-110 mm.

The material in briquettes can easily be reopened by using a very simple machine operating on the principle of a crushing jaw mill.

If the reopened material comes into contact with liquids of whatever type and composition - even in the form of emulsion or suspension and the like - these penetrate through capillary attraction the vacuums, the medullary rays and the vessels, which will expand even beyond the initial volume, maintaining nevertheless the external form of the original fragment, as if the material has a kind of shape memory.

The volume increase takes place gradually when adding the soaking liquid and attains its maximum value with much reduced quantities of liquids. For water, for example, 0.5 kg water per kg kenaf core is adequate. Further additions of liquids will be rapidly and steadily absorbed. Always with the water-kenaf core binomial, the maximum value of water that can be absorbed by spontaneous soaking is 3-4 kg per kg of kenaf core at atmospheric dryness.

The absorption of water by the reopened material is very fast and, in the case of water-kenaf core, is almost immediate.

Even where briquettes are concerned, the absorption of various liquids takes place with similar variations in volume and similar retention of liquids as in the case of pressed and reopened fragments. In this latter instance, however, the times for swelling are longer (from 1 to 20 minutes) and vary principally in relation to the dimensions of the briquettes, the granulometrics of the pressed material and the pressure to which it has been subjected, as well as the nature of the liquid.

In the following Table 1, data are being mentioned that were obtained from a series of tests of compressing and subsequent soaking with water of fragments having original dimensions of 5x20 mm and subjected to pressures varying from 50,000 to 100,000 kPa.

Average data on kenaf core fragment before and after hyper-compression with relation to soaking in water at ambient temperature
Condition of plant dry kenaf core fragments	Dry weight kg	Total weight after water absorption kg	Water absorbed kg	Total volume l	Density apparent g/cm³
Dry at atmosferic dryness	1	-	-	8,3	0,12
Dry after wetting and drying	1	1,5	0,5	8,3	0,18
Hyper-compressed	1	-	-	0,9/1,5	-
Dry fragments reopened after hyper-compression	1	-	-	5	0,22
Wet fragments on reaching max. volume	1	1,5	0,5	10/13	-
Wet fragments at max. water absorption	1	4/5	3/4	10/13	-
Condition of plant dry kenaf core fragments	Density	Specific volume	Dry material moisture
	real g/cm³	apparent cm³/g	real cm³/g	atmospheric %	absolute %
Dry at atmosferic dryness	-	8,3	-	16	19
Dry after wetting and drying	-	5,5	-	43	78
Hyper-compressed	0,6/1,1	-	0,9/1,6	16	19
Dry fragments reopened after hyper-compression	4,5	-	16	19
Wet fragments on reaching max. volume	0,11/0,15	-	6,6/8,6	43	78
Wet fragments at max. water absorption	0,25/0,3	-	3/4	300/400	375/500

A number of applications will now be described in accordance with the material obtained by supercompression of xylem from textile plants or cellulosic raw material, with particular reference to kenaf core, but not intending to consider this a limitation.

Example 1

The use of kenaf core as principal constituent of substrata, whether fertilised or not, for plant production in nursery and gardening or for vegetable-flower-fruit cultivation.

As illustrated in Table 1, supercompressed kenaf, core can absorb a quantity of water 3-4 times that of its weight and if suitable doses of fertiliser and micro-elements are added to the water, these are to a large extent absorbed by the walls of the vacua described earlier, remaining attached with bonds of a chemico-physical nature. The release of those elements is slow and controlled. Consequently, if the kenaf core - duly impregnated with suitable and specific fertilisers for plant cultivation is used as substratum, the nutritive elements, absorbed by the kenaf core, can be used for the vital needs of the plant for a long time - if not for their whole lifetime (annual plants).

The soaking water, or the fertiliser solution, can easily be used again, or modified as the plant requires.

The substrata of supercompressed kenaf core, if correctly processed with additives, constitute therefore excellent substitutes for traditional cultivation-substrata and they also offer the opportunity for new cultivation technologies in the sector of garden nurseries and vegetable-flower-fruit cultivation, with large savings in the cost of plants and operations as compared with traditional technologies.

Example 2

The use of kenaf core as litter for permanent stall-feeding animals (horses, pigs, cows, poultry and other small livestock).

Since long, in the breeding of feathered farmyard species and many other animal species, wide use has been made of sawdust , wood shavings and splinters, as well as wood chips and the like, as litter absorbent of waste matter.

Particularly kenaf xylem is suitable as fragmented litter material for animal breeding because of its high capacity to absorb liquids, its insulating characteristics, its softness thus avoiding the risk of wounding claws, even of newly born chicks of the farmyard avifauna and because of its high degree of elasticity and resistance to compacting, contrary to what happens in the case when wood shavings are used.

For example, three flocks of broilers were bred in an experimental test on one and the same core litter without any major outbreak of diseases - and with a noteworthy economical saving to the breeder.

In the case of breeding pigs on an absorbing litter, also called "deep litter", the absorption capacity of waste liquids and faeces makes it a litter that is decidedly superior to that used until today, consisting of wood shavings and cellulosic scrap such as corn stalks or vegetable left-overs.

Where it concerns horses that are bred for competition, the non-palatability of kenaf xylem prevents them from eating the litter, contrary to what happens when using hay. The animals are completely insulated from the floor, and the elasticity of the litter will not have the unwanted effect of compacting as in the case of wood shavings. Moreover, the fact that core compacts at the points where liquid or solid waste matter has collected, facilitates removal by a simple fork of those parts of the litter that have been dirtied, and simplifies the maintenance of the litter and, therefore, improves the hygienic conditions of breeding. The high absorption ability of the litter confines the contaminated areas and greatly limits the quantities needed for replacement - with a considerable saving to the breeder.

When the litter has finished its use in the animal husbandry, it can be easily re-used for mushroom cultivation, given the easier degradability of kenaf xylem if compared with that of woodshavings (four times higher).

Moreover, kenaf core litter can completely absorb disinfectants and/or preservatives which, apart from guaranteeing a better health of the animals, may allow (as already noted) a long-time use of the same litter, and this will favourably affect profit margins of the breeder since litter replacement costs can be very high, for instance in the case of breading chickens for their meat.

Example 3

Use of supercompressed kenaf core for the absorption of liquid waste of various origins.

The ability of xylem from precompressed textile-fiber and cellulosic-fiber plants to absorb large quantities of liquids has previously been illustrated and quantified; this capacity to absorb can be suitably used to control losses of dangerous liquids such as, for instance, acids, alkalis, mineral oils, etc. from pipes, ships, etc. absorbing or containing them for indefinite periods and allowing their subsequent proper elimination.

Example 4

The use of supercompression in order to reduce the volume of xylem fragments obtained from textile-fiber plants, facilitating transport, storage, preservation.

It is shown in Table 1 that supercompression can reduce the volume of kenaf loose core by 85-90 times, with doubtless advantages when it has to be transported. It is estimated that a specially modified trailer truck can load a maximum of 130-150 cubic meters of loose kenaf core because of its low specific weight; on the other hand, a normal trailer truck loaded with supercompressed briquettes or with loose material derived from briquettes that have been opened can be loaded to the maximum weight capacity allowed for road vehicles.

It has also been noted that, whereas kenaf core in itself is difficult to preserve, as it can be attacked by moulds, mushroom and the like, these dangers do not exist at all in the case of kenaf core in briquettes.

Example 5

Use of kenaf core supercompression and subsequent reswelling with water to augment the core's usefulness as a light filling material or as raw material for production of active charcoal.

From Table 1 it can be noted that supercompressed kenaf core with small amount of liquid swells up again until it reaches a value that is almost the double that of the kenaf loose material as such. That property can be used to good effect in the production of materials for particularly light and ecological filling.

Subsequently, in the reswollen core, the internal surfaces of the vacua, the medullary rays and the vessels can reach twice the value in relation to that of core itself, and are definitely more accessible to possible liquids or gasses with which the fragments come in contact.

That property, if used to good effect, could considerably improve the performance of an active charcoal from kenaf core.

Example 6

Superpressing of kenaf core fragments designated for the production of chemical, semi-chemical and mechanical cellulosic pulps.

The superpressing technology according to the present invention, provides profound advantages to the economics of producing paper pulps from xylem and chipped stems of textile plants, in general, and of kenaf core in particular, because:

the lower volume of the supercompressed material allows storage and use, in an industrial plant of certain dimensions of a quantity that is more than twice as much as when storing and using loose material. Since cooking devices and chemical treatments in general are under pressure, and therefore very costly, the lower cost of plants using superpressed material is of profound value to the economics of the operation;
when using precompressed fragments, the volumetric quantities of the traditionally used solutions and reagents will be drastically reduced. The costs of steam for heating purposes and the cost for storage and pumping are also proportionally reduced;
the liquors and the chemicals they contain are homogeneously distributed on the inside of the pressed fragments and do not remain on the surface thereof as happens in the case of fragments that are not pressed;
the chemical attack of the cooking, therefore, takes place identically at all points of the vegetables, producing paper pulps with generally improved characteristics; particularly, the number of "uncookeds" will be reduced that is to say the number of those fiber aggregates that in the paper jargon are called "splinters" and remain practically unattacked by the chemicals, which negatively influence the mechanical characteristics of the paper and create points of discontinuation, which impairs the characteristics for the use in newsprint;
the better distribution of liquors results in comparatively less consumption of chemicals, a higher pulp yield and less pollution of refluent waters.

A complete series of tests has made it possible to quantify (see Table 2 and Table 3) the advantages derived from the supercompression of kenaf fragments used in the production of CTMP (Chemio-Thermo-Mechanical Pulps) and semi-chemical pulps.

Advantages of hyper-compression of kenaf fragments used in the production of CTMP pulps
		Kenaf (Hibiscus cannabinus)
Characteristics	Units	Untreated	destructured by hyper-pression
		core	whole stem	core	whole stem
Freeness	SR	32	42	26	41
Breaking index	Nm/g	18	52.2	58	60.3
Burst index	kPa m²/gr	0.7	2.3	2.3	3.1
Tearing index	mN· m²/g	2.2	4.5	3	8.1
Yield	%	70	70	75	75

Advantage of hyper-compression of kenaf fragments used in the production of semi-chemical pulps
Characteristics	Units	Kenaf Hibiscus cannabinus L.
		untreated	hyper-compressed
Freness	SR	33	37
Breaking index	Nm/g	55.2	74.9
Burst index	Kpa m²/g	2.5	4.4
Tearing index	mN· m²/g	3.9	7.9
Yield	%	58	62

Now, by the way of examples, will be described the equipment and the technologies used in connection with the present invention for the pressing of xylem from textile plants or cellulosic plants with particular reference to the processing of the kenaf core.

The superpressing of the xylem of textile-fiber or cellulosic-fiber plants requires that the material to be treated reaches the operating machines in the right condition of size and cleanliness needed for the intended use. Separation of the xylem from the other parts composing the vegetable, the elimination of various contaminating matters like leaves, dust, parenchymatous cells and, in some instances, also pith, and its reduction in sizes considered suitable, are rather well-known operations. A process and an adapted machinery system has been described in an earlier patent application by the same applicant.

The superpressing plant is in fact conceptionally simple as is illustrated in Figure 1. It consists of a silo with a flat base 1 of sheet metal of the type normally used in the corn industry. At the base of the silo operates a screw feeder which, whilst turning, transports the fragments to be treated to the central discharger. Those fragments, upon leaving the silo, are picked up by a system of transport by screw feeders 2 and will be moved to a loading hopper feeding a multihead hydraulic press 3. Each head is preceded by an introductory screw feeder, pushing the vegetable matter to be treated to an advance chamber that will dose automatically once the material has entered.

Subsequently, the actual pressing element, consisting of a hydraulic cylinder, pushes the material into a shaped conduct which has sections that decrease in size towards the exit. The narrow passage of the duct can be regulated by means of mobile walls operated by a pincer also this through hydraulic action. By using the pincer, the effective pressure on the vegetables being processed can be brought to 100,000 kPa., thus regulating the desired destructurisation of fragments.

Energy consumption by the pressing operation is around 0.15 kWh/kg. The material compressed into briquettes is removed by means of step-conveyors 4 and can be preserved indefinitely without any particular precaution. If for some particular use the superpressed material should be flaked, this flaking can be carried out directly at the exit of the pressing system with a breaker or jaw-crusher 5 or something similar; the energy consumption for that operation is negligible.

In view of the simplicity and linearity of the described processing, the whole plant can be operated automatically with a computerised program.

What has been described above is a batch, i.e. not continuous process.

Still in the context of the present invention, a continuously processing type is envisaged in which the vegetable material to be treated is transported by way of conveyor belts provided with banked conveyors with a fixed deflector or a continuous belt travelling towards a roller-pressure unit, preferably with rollers of the "pilgrim-process" type, the technology of which is well known in the steel industry. That technology is necessary considering the very high degree of volume reduction for which the conventional type of presses or calenders would not be suitable.

The compressed material at the outlet of the roller-pressure unit can be cut into briquettes by a cutting unit of the "travelling" type.

Alternatively, a flaked product can be obtained by moving the material to a jaw-breaker placed at the exit of the pressing unit or to a fixture with rollers shaped like clod-breakers or something similar, carrying out agglomeration prevention in a continuous operation.

That piece of equipment is not described in detail as it concerns a technical transfer well known noted separately in another industrial field.

Summarising, the present invention concerns a new technology for the treatment of the xylem of annual or polyannual textile-fiber or cellulosic-fiber plants by greatly modifying the internal structure of the xylem by mechanical compression actions.

As a result it will break down in a manner that will favourably alter its proprieties and characteristics, particularly the volume and the capacity to swell again by spontaneous soaking with pure liquids, solutions, emulsions, suspensions, etc.

A number of examples using the technology in question have been reported previously. These have been conducted on kenaf xylem since it is expected that that type of raw material will be easily available in the near future.

The examples given should not be considered limiting in any way in the context of the current industrial patent right.

Claims

The process for mechanical treatment of woody products from annual and polyannual plants including preparing xylem fragments from textile- or cellulosic plants in dry condition, characterised by the step of subjecting said fragments to the mechanical pressing in order to provoke the breaking down of the macroscopic structure and the destructuring of the vessels and medullary rays.
The process according to Claim 1, characterised in that mechanical pressing is exerted to provoke a reduction in volume of the original material up to 10-25%.
The process according to Claim 1 or 2, characterised in that the pressed material is subjected to a disaggregation operation.
The process according to one or more of the preceding claims, characterised in that the woody product of textile plants or of cellulosic fiber is formed by kenaf xylem.
The product obtained through processing according to one or more of the preceding claims, characterised in that the compressed material is moulded into the shape of compact briquettes.
The product obtained through processing according to one or more of the claims from 1 to 4, characterised in that after compacting the pressed material is subjected to mechanical shaping.
The use of the material obtained according to one or more of the preceding claims for capillary absorption of pure liquids, or solutions, or suspensions, or emulsions.
The use of the material obtained according to one or more of the claims 1 to 6, characterised by the fact that it is used, after having absorbed liquids, as an agent for the slow release of liquids.
The use of the material obtained according to claim 8, characterised by the fact of using it as substratum for cultivation purposes.
The use of the material obtained according to claim 8, characterised by the fact of using the substratum for cultivation after introducing therein nutrients.
The use of the material obtained according to one or more of the claims from 1 to 6 as a staffing material for producing activated charcoal.
The use of the material obtained according to one or more of the claims from 1 to 6 for absorbing and capturing aggressive or damaging liquids in the industrial field, or for protecting the environment.
The use of the material obtained according to one or more of the claims from 1 to 6 as raw material for the paper or paper-technical industry
The use of the material obtained according to one or more of the claims from 1 to 6 as soundproofing material.
The use of the material obtained according to one or more of the claims from 1 to 6 as heat insulating material.
A plant for producing the material obtained according to one or more of claims 1 to 6, designated for uses according to one or more of claims 7 to 15, characterised by the fact that it includes:

means for moving the material towards a hydraulic pressing unit arranged so that it exerts such a pressure that the macroscopic structure of the material is broken down;

means for moulding into briquettes, placed at the exit of the pressing unit.
A plant according to claim 16, characterised by the fact that it includes crushing means, fed by the material in briquettes, to obtain compressed although broken-up material.
A plant for continuous production of materials according to one or more of the claims from 1 to 6, designated for uses according one or more of claims 7 to 15, characterised in that it includes continuous pressing means, including rolling means, consisting of the "pilgrim-process" type.
A plant according to the claim 18, characterised in that the material leaving the rolling means is subjected to crushing by shaped rollers.