IE48534B1 - An improved method of producing a fibrous mass from peat and means for carrying out the method - Google Patents

Abstract

The present invention relates to a method of producing a fibrous mass from peat. It has not been possible in the past to produce an easily dewaterable fibrous mass from peat when using in the production a continuous process which (1) could be carried out with a minimum amount of manpower, (2) enables a higher yield from the peat moors than had been the case before, (3) enables an efficient separation of colloids and particles smaller than 0.2 mm, and (4) dt enables the use of a simple equipment which, by a quickly made replacement of a screening member, can be changed to match the nature of the dug-up peat. The object of the present invention was to obviate this problem which, according to the invention, is realised substantially by the features that, after a primary sorting operation, the peat-material suspension is liquid-concentration regulated by supplying thereto an amount of liquid depending on the degree of humification of the dug-up peat, and then supplying the suspension under pressure to at least one screening member having a permeability depending on the peat-fibre concentration of the peat-material after said concentration regulation.

Description

The present invention relates to a method of producing a fibrous mass from peat, comprising carefully exposing the fibres of the peat-fibre material and transferring the same into a peat-material suspension which is subjected to a grading (or: screening, classifying, assorting) operation.

It has not been possible in the past to produce an easily de-watered fibrous mass from peat, while using in the production a continuous process which (1) could be carried out with a minimum of manpower requirements, (2) enables a greater yield from the peat-moors than had been the case before, (3) enables an efficient separating out of colloids and particles less than 0.2 mm, and (4) enables the employment of a simple installation which, by a quickly made replacement of a screening member, can be changed to match the character of the digged-up peat.

The present invention has for its object to obviate these problems, and this, according to the invention, is mainly realized by the fact that, after a primary sorting step, the peat-material suspension is subjected to a liquid concentration (or consistency) regulation by supplying thereto an amount of liquid depending on the degree of humidification of the digged-up peat, and then supplying the suspension under pressure to at least one screening member having a permeability depending on the peat-fibre concentration of the peatmaterial suspension after said concentration regulation.

The present invention has also for its object to provide simple means for carrying out the above-described process.

The present invention provides a method of producing a peat-fibre concentrate comprising the steps of: a) measuring the degree of humification of raw peat on a peat moor; b) excavating peat from the peat moor; c) suspending excavated peat in water to give a peat-fibre concentration of from 1 to 6% by weight; - 2 48534 d) subjecting the peat suspension from step c) to a primary sorting operation wherein material having a size greater than about 10 mm is removed from the suspension; e) adjusting the peat-fibre concentration of the sorted peat suspension from step d) by adding to the suspension, water, not containing any peat fibre, and devoid of any suspended particles in an amount sufficient to provide a selected peat-fibre concentration of less than 1.0% by weight depending upon the initial degree of humidification of the raw peat; f) subjecting the peat suspension obtained from step e) to a secondary sorting operation by passing the suspension through a screening member having a selected permeability depending upon the adjusted peat fibre concentration of the peat suspension from step e) to produce a concentrated peat-fibre suspension and a substantially fibre-free effluent containing colloids and particles less than 0.2 mm in size.

Preferably, the method of the invention additionally comprises the steps of: g) separating organic matter from the substantially fibre-free effluent produced in step f), and h) dewatering the separated organic matter.

Generally, the separation of the organic matter from the effluent in step g) above is effected in a two stage sedimentation process comprising a first sedimentation stage from which a suspension containing from 4 to 10% by weight dry substance is obtained and a second sedimentation stage from which a suspension is obtained which, after dewatering, has a dry substance content of from 12 to 25% by weight. - 3 48534 The inventive method will be described more in detail hereinafter with reference to the accompanying drawing which is a diagrammatic illustration of a plant for producing a fibrous mass from peat. The diagrammatically illustrated plant comprises a carriage 1 or the like which can be moved on a peat-moor. The carriage 1 carried a pump 2 having at least one spray nozzle (not shown) emitting a water jet for defibrating peat material on the moor. The pumpable peat material suspension thus obtained (having a peat-fibre concentration of 1 to 6% by weight) is taken up by means of a take-up pump 3 and is conveyed by the latter through a conduit 4 to a primary sorting assembly 5 comprising for example, at least one rotary perforated screen· having a central or inject intake for the incoming stuff/. In the primary sorting assembly 5, material greater than about 10 mm in size is separated, involving that about 10 to 20% of the peat material of the suspension is separated out (through conduit 6 in the drawing). The material separated out (i.e. or reject) the rejected stuff,/ias a peat fibre concentration of about 6% and is suitable, for example, for burning or for soil-improvement purposes, or accept, The accepted stuff,/obtained after the primary sorting assembly 5 is a suspension with pumpable consistency because a very small proportion only of the liquid has been removed in the primary sorting assembly 5.' This suspension, which contains fibre particles smaller than about 10 mm, including colloids and particles smaller than 0.2 mm, is passed through a. conduit 7 to a liquid supplying assembly 8 comprising; for example, a collecting tank with a water inlet 9.

In the liquid supply assembly 8 a liquid, suitably water, is supplied in an amount such as to impart to the peat material suspension a peat-fibre concentration less than 1%· by weight. The higher degree of humidification of the peat-material of the moor, the more water is supplied in order to obtain a lower peat-fibre concentration.

Humidification is a definition of how much the peat is degraded. The degree of humidification increases with increasing degradation of the peat.

Von Post's scale, which is described in Planeringsrapport, Torv i Sverige 1977:1, a planning report made by the NSmnden ftir Energiproduktion:s Planning Board for Peat, gives a dimensionless numerical value for the degree of humidification.

From the table below it will be seen what peat-fibre concentration is aimed at by supplying water at different degrees of humidification (H) of the raw peat material from the moor: Degree of Humidification Water supplied in the Water Supply Assembly to reach the following peat-fibre concentration of the suspension: 0 to 3 max about 1% by weight 3 to 6 max about 0.75% by weight above 6 max about 0.5% by weight The consistency regulated peat-fibre suspension, which thus has a peatfibre concentration lower than about 1% by weight, is supplied through a conduit 10 to an assembly 11 for separation colloids and particles smaller than about 0.2 mm. This assembly 11 comprises for instance a screening member having through flow perforations about 1 mm in diameter, or smaller.

The size of the through-flow perforations of the screening member of the assembly 11 is determined in relation to the concentration of the suspension and the degree of humidification of the peat material. The more humidified peat in the suspension and the lower its concentration, the smaller the perforations of the screening member should be in order to obtain the greatest possible yield of accept, i.e. the maximum possible amount of easily drainable peat-fibre material. - 548534 From the following table it is seen what yield of easily drainable peatfibre mass can be obtained at various degrees of humidification, various peatfibre concentrations and various perforations or mesh sizes of the screening member of the assembly 11: Degree of humidification (H) (according to von Post's scale) Peat-fibre concentration in % by weight Hole or mesh size of screen (mm) Yield % 0-3 0.75-1 about 1 about 90 3-6 0.5-0.75 0.5 - 1 about 80-90 above 6 0.1-0.5 max. 0.5 about 70-90 fine-mesh net or cloth It is seen from this table, that it is possible to obtain a very high 10 yield (i.e. usable proportion of the completely treated peat), independently of 1 degree of humidification of the peat moor simply by supplying a suitable amount of water to obtain a suitable peat-fibre concentration, and by using in the assembly 11 a screening member having an adequate hole or mesh size.

At a peat fibre concentration in excess of about 1% by weight and a larger mesh size of the screening member than 1 mm, an essentially lower yield will be obtained, and at higher peat-fibre concentrations and constant mesh size, for example, there will be a great danger of clogging the plant, resulting in a breakdown of the operation of the mill.

By utilizing in the process the values listed in the last-mentioned table, 2q a peat-fibre concentration increase of at least 100% will be obtained in the assembly 11, involving that about 50% of the water supplied is removed, thereby removing also at least 50% of the colloids and particles smaller than about 0.2 mm (through the conduit 12, possibly for returning to the moor).

The peat-fibre concentration of the suspension after the assembly 11 has 25 a maximum of about 2% by weight, and the suspension now has a character such that it can be passed (through a conduit 13) to and received by a take-up assembly 14 comprising an ordinary take-up filter, whereby the peat-fibre . 6 48534 concentration can be increased in a simple way to about 10% by weight, and, in addition, at least 75% of the remaining colloids and particles smaller than about 0.2mm are carried away with the effluent water (which flows away through the conduit 15, possibly for returning to the moor). The accept stuff obtained is carried away through a conduit 16 to be used, for instance, for papermaking, as a substance for cleaning purposes, for increasing the dry-substance content of various reject stuffs, as a fuel or as a soil improvement substance, or fertilizer.

Thus by utilizing the method described, a peat-fibre concentration increase from lower than 1% by weight to about 10% by weight will be obtained. In practicing the production method of the invention, of course, more than one primary sorting assembly or unit 5 and more than one secondary sorting assembly or unit 11 can come into use.

It is advantageous to add the water (or other suitable liquid) after the primary sorting unit 5. It is essential that the water supplied through the conduit from the water supply unit is devoid of suspended particles. In other words: it is not suitable to use water directly from the peat moor, but this water will have to be cleaned from suspended /particles, since otherwise the effect of the following separation process would be reduced. an To provide/extremely simple equipment for carrying out the method of the invention, the primary sorting unit 5 comprises a screening member, preferably in the form of a rotary drum 5a with perforations 5b of a diametrical size of about 10 mms. The peat-material suspension is passed into this drum by the conduit 4, the rejected stuff being passed out from the drum 5a through the conduit 6, while the accept stuff is obtained by retaining the suspension passing through the perforations 5b. This accepted stuff is carried away through the conduit 7 and through the liquid supply unit 8 after supplying liquid through the conduit 10 to the secondary sorting unit 11. The latter comprises at least one stationary screening member Ila having perforations or holes 11b the sizes of which . 48534 can vary as stated in the table referred to hereinabove. In the present case the portion of the suspension which cannot pass through the screening member 11a is retained as accepted stuff and is passed further through conduit 13, whereas the portion of the suspension passing through the screening member Ila is removed as rejected stuff through conduit 12.

Peat material treated according to the inventive method, and preferably with the employment of the inventive equipment, can, without any difficulties, by mechanical drainage and without any supply of heat have imparted to it a peat-fibre concentration of about 40 to 45% by weight.

IQ The sorting or classifying operation can comprise more than one primary sorting step and more than one secondary sorting step. The primary and secondary sorting steps may be carried out in one single sorting or classifying unit, for instance at different positions in one single screening assembly.

The circuitry of the plant may be provided with or replaced by pressurizing elements (not shown and not described in detail, since pressurizing elements of any type previously known to those skilled in the art may be used) to supply the diluted suspension under pressure to the screening unit 11 (preferably being a so-called arc screen).

It may be mentioned, finally, that the expression particles smaller than about 0.2 mms. involves particles which totally are of sizes smaller outer than 0.2 mms., but preferably also particles whose smallest/dimensions are about 0.2 mm, but whose largest outer dimensions may be larger.

Thus, for instance, a particle comprised by this conception may have a length substantially larger than about 0.2 mm, but a width less than about 0.2 mm.

The suspension effluent passing through conduit 12 and/or conduit 15 is substantially fibre-free but contains organic materials (predominantly colloids and particles smaller than 0.2 mm) from the peatmoor, which remain after the primary sorting step and the fibre separation following thereafter. This substantially fibre-free effluent is subjected to a separation process to separate the organic matter. The dry-substance content of the thus separated organic matter is increased by dewatering the same. The organic matter thus dewatered, after storage and/or transport may suitably again be mixed with water to be spread out over a ground area, for instance, to serve as a soil melioration agent and/or to form a covering layer serving, i.e., to preserve humidity in the underlying soil.

The organic matter is suitably separated out of the fibre-free suspension by a sedimentation process, the sedimentation being brought about causing the peat-fibre concentration of the peat-material suspension to be less than about 0.5% by weight when the degree of humidification of the digged-up peat is higher than 6 according to von Post's scale. In the last sedimentation step it may be suitable to add a flocculent, preferably a polymer, alum or other salts, in order to accelerate the sedimenting effect.

The separation of organic matter from the substantially fibre-free effluent may suitably be carried out in a plant of the type shown in Fig. 3.

This plant comprises a settling basin 17 into which the fibre-free suspension is supplied through the conduit 12 and/or 15. In this settling basin the organic matter is allowed to settle to the bottom, and the water, in a wellknown manner, is allowed to flow off at the top edge of the basin 17 and is carried away through gutters or chutes 18. The organic matter collected in the bottom portion of the basin 17 is pumped by a pumping equipment 19 through a conduit 20 into a second settling basin 21, the pumped suspension containing - 9 48534 to 10% dry substance by weight, preferably 5 to 7% dry substance. In order to obtain efficient sedimentation, the settling basin 21 is provided at its top with laminae 22 arranged in a manner previously known per se over which water can pass before flowing over the top edges of the basin 21 to be passed away in a purified state through effluent channels 23. In order to accelerate the sedimentation efficiency in the basin 21, a flocculating agent, for instance a polymer, alum or other salts may be supplied from a tank 24 to increase the weight of the organic particles so that they will sink at a greater velocity. The organic matter collected in the bottom portion of the basin is pumped out from the basin 21 by a pump equipment 25, and the pumpable suspension is furnished through a pipe line 26 to a dewatering station 27. At this station the suspension is dewatered, for instance by a pressing and/or centrifuging process, until the accepted stuff, the accept, has a dry-substance content of at least 10% by weight and up to 25% dry substance. The high dry-substance content now obtained has the advantage that the accept (shown as a block and designated by 28) will be handy, that it can be stacked in a space-saving manner without any need of particular storage equipments, and that it can be transported at lowcost for further use.

The material blocks 28 are conveyed in their dry condition to a utilization area 29 where it is mixed with water so as to be spread out together therewith. At the utilization area 29 the blocks 28 may be supplied into a container 30 with water in which the blacks 28 readily dissolve. The container 30 is connected through a conduit 31 to a water25 carrying conduit 32 of a conventional irrigation plant 33, whereby organicmatter-containing water will be drawn up by ejector action from the container 30 and supplied to the stream of water flowing in conduit 32. The water admixed with organic matter is sprayed through nozzles 34 over a field 35 and is -10 48534 deposited as a thin film 36 on this field. The film 36, when dried, may have strength enough (depending on the concentration of the organic matter), for it to be utilized in preventing wind erosion and in preserving humidity in the underlying soil. It further has soil-melioration properties and thus can be used as a soil-me!ioration agent, in which case it is mixed with the organic dry-substance in a manner to cause 10 to 20 g dry-substance to be spent on each square meter of the field surface. The film also is well adapted to coat sown seeds, particularly when they lie superficially and are especially sensitive during the germination period. (0 In order to increase the dry-substance content of the accept-stuff obtained from the separation process, the latter may have dry-substance 37 added to it, for instance peat-substance from the same peat moor 38 from which the peat fibres, too, have been taken. Said dry-substance 37 may be added instead of pressing and/or centrifuging or in combination therewith.

Portions of the dewatered accept stuff can be used for producing material for combustion purposes or for lubrication purposes, or as raw materials for chemical industry or as additives in casting.

The separation process described hereinbefore is suitably a sedimentation process, but other methods for separating the organic material can also be applied.

The inventive methodology implies the advantage that not only the peat fibres, but also smaller particles are made use of so that the peat-fibre extraction will only reject roots and other larger components of the peat moor and pure or substantially pure water. These remnant products may be disposed of (for example returned into the peat moor) without any danger of interference with the natural environment.

Claims (5)

1. A method of producing a peat-fibre concentrate comprising the steps of: a) measuring the degree of humidification of raw peat on a peat moor; b) excavating peat from the peat moor; 5 c) suspending excavated peat in water to give a peat-fibre concentration of from 1 to 6% by weight; d) subjecting the peat suspension from step c) to a primary sorting operation wherein material, having a size greater than about 10 mm, is removed from the suspension; 10 e) adjusting the peat-fibre concentration of the sorted peat suspension from step d) by adding to the suspension, water not containing any peat fibres, and devoid of suspended particles in an amount sufficient to provide a selected peat-fibre concentration of less than 1.0% by weight depending upon the initial degree of humidification of the raw peat; 15 f) subjecting the peat suspension obtained from step e) to a secondary sorting operation by passing the suspension through a screening member having a selected permeability depending upon the adjusted peat fibre concentration of the peat suspension from step e) to produce a concentrated peat fibre suspension and a substantially fibre-free effluent containing colloids and 20 particles less than 0.2 mm in size.

2. A method according to Claim 1, wherein the initial degree of humidification of the raw peat, according to Von Post's scale, is from 0 to 3; the amount of water added in step e) is sufficient to adjust the peat-fibre concentration to a value of from 0.75 to 1% by weight, and the screen member in 25 step f) is selected to have perforations of about 1 mm in diameter.

3. A method according to Claim 1, wherein the initial degree of humidification of the raw peat, according to Von Post's scale is from 3 to 6; the amount of - 12 48534 water added in step e) is sufficient to adjust the peat-fibre concentration to a value of from 0.5 to 0.75% by weight, and the screen member in step f) is selected to have perforations of from 0.5 to 1 mm in diameter.

4. A method according to Claim 1, wherein the initial degree of 5 humidification of the raw peat, according to Von Post's scale, is greater than 6; the amount of water added in step e) is sufficient to adjust the peat-fibre concentration to a value of from 0.1 to 0.5% by weight, and the screen member in step f) is selected to have perforations not greater than 0.5 mm in diameter. 10 5. A method according to any one of Claims 1 to 4, wherein step f) is effected by passing the suspension under pressure through the screening member. 6. A method according to any one of Claims 1 to 5, further comprising the steps of: , 5 g) separating organic matter from the substantially fibre-free effluent produced in step f), and h) dewatering the separated organic matter. 7. A method according to Claim 6 wherein the separation of the organic matter from the effluent is effected in a two stage sedimentation process 20 comprising a first sedimentation stage from which a suspension containing from 4 to 10 weight percent dry substance is obtained, and a second sedimentation stage from which a suspension is obtained which, after dewatering, has a dry substance content of from 12 to 25 weight percent. 8. A method according to Claim 7, wherein a flocculating agent is 25 added to the second sedimentation stage to enhance the separation of the organic matter from the effluent. - 13 48534 9. A method according to Claim 8, wherein said flocculating agent is a polymeric flocculating agent. 10. A peat-fibre concentrate whenever obtained by a method as claimed in any one of Claims 1 to 9.

5. 11. A method of treating soil comprising mixing, with water, a fibre-free organic matter obtained by a method as claimed in any one of Claims 5 to 9, and spraying the resulting fibre-free aqueous mixture onto the soil to be treated.