Method and plant for separation of wax and fibers from plants

Abstract

A method and an plant for separating wax from a dried wax coated plant material, comprising mechanically processing the plant material in a dry process by using an apparatus adapted for deforming at least the outer surface of the plant material, so that the wax coating is cracked and released from the remaining, partly de-waxed, plant material; separating the plant material in a separator into a portion A comprising plant material with a relatively high content of cracked and released wax coating and a relatively low content of the remaining, partly de-waxed, plant material, and a portion B comprising respectively a relatively low content cracked and released wax coating and a relatively high content of the remaining, partly de-waxed, plant material; liquefying the wax contained in portion A, and separating the liquefied wax from the remaining, partly de-waxed, plant material in portion A.

Claims

1. A method for separating wax from a dried wax coated plant material, comprising the steps of: a) mechanically processing the plant material in a dry process by using an apparatus adapted for deforming at least the outer surface of the plant material, so that the wax coating is cracked and released from the remaining, partly de-waxed, plant material, b) conveying the plant material in a dust proof tube, c) separating the plant material in a separator into a portion A comprising plant material with a relatively high content of cracked and released wax coating and a relatively low content of the remaining, partly de-waxed, plant material, and a portion B comprising respectively a relatively low content cracked and released wax coating and a relatively high content of the remaining, partly de-waxed, plant material, d) liquefying the wax contained in portion A, e) separating the liquefied wax from the remaining, partly de-waxed, plant material in portion A, wherein the plant material is conveyed in the dust proof tube via suction applied to the separator.

2. The method according to claim 1, wherein the wax in portion A is liquefied by a process comprising adding an aqueous liquid to said portion A.

3. The method according to claim 1, wherein said mechanical processing of the plant material further comprises cutting the plant material to comminuted plant material.

4. The method according to claim 1, wherein said mechanical processing of the plant material further comprises milling the plant material.

5. The method according to claim 3, wherein said separator comprises a sieve having sieve openings adapted for retaining said portion B on one side of the sieve, and allowing said portion A to pass the sieve.

6. The method according to claim 5, wherein said portion A is forced through the sieve by suction.

7. The method according to claim 5, wherein said milling is performed before said separating the plant material in said separator into said portion A.

8. The method according to claim 2, wherein the wax is subsequently separated from the aqueous liquid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Is a flow diagram showing a process as well as a setup for a processing plant according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

(2) “Straw” means the remains of a agricultural plant, e.g. a cereal, after the seed head has been removed, i.e. the leaves and the stem/stover (nodes and internodes). Straw may also mean the whole of a high energy grass, such as for example elephant grass.

(3) “Feedstock” means the plant material applied to mechanical treatment.

(4) “Straw fibers” and “mill generated fiber” mean the fraction of mechanically treated feedstock enriched in fibers and low in wax content.

(5) “Mill generated fines” means the fraction of mechanically treated feedstock enriched in wax content and low in fibers content.

(6) “Straw fines” means the fiber fraction of mill-generated fines.

(7) As mentioned above, wax is a surface component on leaves and the stem of most plants. The present invention may be applied to most kinds of plant feedstock comprising wax. In the following, however, a preferred embodiment of a processing plant and method is disclosed being adapted especially for the purpose of illustrating the invention used for processing wheat straw.

(8) Wheat straw contains a substantial amount of wax, and is available in high amount as bio-waste from agriculture. Furthermore it is an example of a feedstock for production of biofuel where wax is a component which needs to be removed in a pre-treatment before fermentation. Other feedstock may be treated in the same way, or with minor modifications obvious to the skilled person.

(9) According to FIG. 1 the mechanical treatment comprises at least a straw shredding and a straw milling process. First the dried straw material is supplied by conveying bales of dried straw to a straw shredder adapted for shredding the straw into shorter straw parts having an average length between 2 and 15 cm.

(10) Thereafter the shredded straw is preferably passed through a stone trap for removing unwanted solids, such as stone, sand or soil, and to a straw mill for milling the short straw parts. Hereby the straw parts are deformed significantly and especially the surface of the straw material is deformed, so that a significant part of the wax on the straw surface is cracked and relieved from the straw part during the milling process.

(11) In this relation the milling apparatus may comprise hammer mill and/or a disc mill or any other mill or combination thereof. In the preferred embodiment however, at least one disc mill is used.

(12) In view of the present invention it will be apparent to the skilled person that the more the straw is deformed the more wax will be relieved from the straw material, and thereby it will be easy for the skilled person to suggest different mill constructions or combinations thereof by simple trial and error and for the purpose of efficiently milling the straw material in order to have as much wax as possible relieved from the straw material.

(13) The milled straw material, comprising both a portion of straw fibers and a portion of mill generated fines is then conveyed to a separator adapted for substantially separating the straw fiber to a portion B (referenced “B” in the drawing) and the mill generated fines to a portion A (referenced “A” in the drawing), In this embodiment, being optimized for processing wheat straw the separator comprises a sieve arrangement, preferably a rotary sieve, being adapted for primarily separating the intermodal parts of the milled straw material from the rest of the milled straw material.

(14) Hereby a volume of relatively short intermodal straw parts are obtained, being relatively free from wax coating on the surface. Due to its reduced wax coating, and thereby its increased absorbency such intermodal straw parts are very suitable as box straw material for various livestock, or for second generation bioethanol production.

(15) The rest of the milled straw material is then transferred to a second part of the separator comprising e.g. a suction based dust separator, a cyclone or the like, being adapted for separating dust material including wax dust and particles from e.g. the straw nodal parts and leaves.

(16) In view of the present invention it will be apparent to the skilled person that other types of separators may be used for the same purpose of separating the straw material into a portion B having a relatively low wax content, and a portion A having a relatively high wax content.

(17) The straw nodal parts and leaves are hereby suitable for different products, such as straw brickets, pellets or the like.

(18) The wax dust and particles (portion A) are hereafter according to the invention used in a liquid extraction process, e.g. by dissolving the wax using e.g. Dichloromethane, Chloroform, Ethanol or heated water.