Solid material comminution or disintegration – Processes – With application of fluid or lubricant material
Reexamination Certificate
1998-04-30
2001-07-17
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Processes
With application of fluid or lubricant material
C241S024200, C241S028000, C241S081000
Reexamination Certificate
active
06260777
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and equipment for manufacturing predetermined low bark content wood chips and a high bark content fuel fraction from wood chips with bark attached. More specifically the method includes a mechanical bark removal process, pre-cleaning of wood chips with bark attached, and final cleaning of the flow of wood chips, with the aid of an optical separator.
BACKGROUND OF THE INVENTION
A wood bark manufacturing method is known from international patent publication WO 93/25324. According to this, the wood chips with bark attached are ground initially either with a special plate grinder, or with a vibrating cone crusher, wherein the bark separates from the wood chips and the size of the bark particles diminishes. Thereby, the bark can be separated more easily during later separation stages. A grinder or a vibrating cone crusher is followed by pneumatic separation, to separate outer birch bark, after which sawdust is removed using a vibrating sieve. The bark content has now dropped to considerably less than 10%, and the final cleaning can be carried out using an optical sorter. According to the patent, two optical sorters are used in series, but can, however, be replaced by a single more powerful device. The accepted fraction from the second optical sorter is led to grinding and the reject to the fuel fraction.
Equipment that is essentially that described by the application has been built in Kankaanp{umlaut over (aa)} in Finland, the supplier being BMH Wood Technology Oy. In the commercial equipment, a magnetic separator and a pneumatic separator are used in the pre-cleaning to separate metal scrap and stones. Sawdust is removed from the commercial equipment before grinding, and after grinding the vibrating sieve is replaced by a so-called pocket-roll sieve (a roller sieve developed especially for sieving sawdust). In the commercial equipment, a good yield is achieved with a bark content of about 1%, which is sufficiently clean for the manufacture of certain grades of cellulose. The yield varies between 60-70%, depending on the species of timber and other factors. If cleaner chips are wanted, the yield drops, and correspondingly improves with a poorer level of cleanliness.
SUMMARY OF THE INVENTION
An object of the present invention is to achieve a better yield than previously at each corresponding level of cleanliness.
The characteristic features of the method for manufacturing predetermined low bark content wood chips and a high bark content fuel fraction from wood chips with bark attached, includes the steps of:
mechanical bark removal treatment, in which the bark is removed from the chips and their size is reduced,
pre-cleaning of the flow of chips with bark attached, into a flow of chips with a bark content of less than 10% and high bark content rejects, with the aid of pneumatic and mechanical sieving,
final cleaning of the aforesaid wood chip flow from the pre-cleaning, with the aid of an optical separator, to create low bark content wood chips and a fraction with a higher bark content, and
collection of the rejects leaving the process, to create the aforementioned high bark content fuel fraction, characterized in that before the mechanical bark removal process, a predetermined thin fraction of the chips, is sieved out of the flow of wood chips, and then bypasses the debarking process.
The mechanical bark removal process may take place by means of a grinder, press-rollers, or a crusher. Alternatively, the mechanical bark removal takes place using a blade ring chipper, which cuts the wood chips into smaller pieces, while removing the bark.
According to the method, 20-100% of the fraction with a higher bark content obtained from the optical separator is directed to the fuel fraction, and correspondingly 80-0% is returned to the mechanical bark removal process. The optical separator includes a pneumatic conveyor and a division plate, by means of which the flow of chips is divided first into the said wood chips with a low bark content and wood chips with a higher bark content and further the latter part is divided with the aid of the division plate directly into a fuel fraction and the said part that is returned.
The method may include a pre-separation step before the thickness sieving step, in which the oversized wood chips, stones, and metals are removed from the wood chips with bark attached.
The flow of wood chips from the mechanical bark removal process and the thin chip fraction from the thickness sieving may be sieved using a mechanical sieve, to remove sawdust as a third reject and using a pneumatic separator to remove light birch bark, leaves, needles, and other airborne material as a fourth reject.
Equipment for manufacturing wood chips with a low bark content from wood chips with bark attached, which equipment includes mechanical bark removal devices and pre-separation devices consisting of a mechanical and a pneumatic separator and an optical sorter. The equipment is characterized in that it includes a wood chip thickness sieve located before the mechanical bark removal devices and a correction line connected to the exit of the thin fraction obtained, by means of which the thin fraction is taken past the mechanical bark removal devices to the pre-cleaning devices.
The mechanical bark removal devices may consist of at least one of a blade ring chippers, a grinder, a press roller, and a crusher.
The distribution values of the wood chip fractions according to the accompanying table are, to a great extent, the point of departure of the invention:
Sieve
Fraction
Clean
Wood
Bark % of
gap
remaining
wood chips
chips
wood chips
mm
in sieve %
in fraction
with bark
with bark
0
5,03
2
16,73
79,03
1,96
3,61
4
37,94
89,98
2,72
8,57
6
25,37
85,54
7,15
16,78
8
8,01
74,54
14,83
19,98
10
6,92
69,00
25,51
18,30
It is surprising, that in the smallest fractions (sieve gap 4 mm, or less), there is not much bark attached to the chips, whereas in chips above this size the proportion of chips with bark attached is considerable. Because mechanical processing in any event reduces the size of the wood chips across the board, it is advantage s to separate this fairly clean part of the wood chips and have it bypass the mechanical processing. There is bark as such even in the smallest chips, but it is loose, and most of it leaves during the separation of the sawdust, which has been moved so that it takes place after the mechanical processing.
These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings, which show schematically one plant according to the invention and the method used in it.
REFERENCES:
patent: 4036440 (1977-07-01), Makila et al.
patent: 4332353 (1982-06-01), Lario et al.
patent: 5000390 (1991-03-01), Marrs
patent: 5137621 (1992-08-01), Brown
patent: 5577671 (1996-11-01), Sappanen et al.
patent: 5709257 (1998-01-01), Vinogradov et al.
patent: WO 93/25324 (1993-12-01), None
Fildes & Outland, P.C.
Rosenbaum Mark
Valtion teknillinen tutkimuskeskus
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