WO1999020717A1

WO1999020717A1 - Method and device for manufacturing composite fuel bodies

Info

Publication number: WO1999020717A1
Application number: PCT/SE1998/001859
Authority: WO
Inventors: Zargham Niazi
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-10-21
Filing date: 1998-10-16
Publication date: 1999-04-29
Anticipated expiration: 2000-04-21
Also published as: AU9563798A; SE9703830L; SE511292C2; SE9703830D0

Abstract

The present invention concerns a method and a device for manufacturing composite fuel bodies such as briquettes and similar that include one or more solid combustible materials. The method for manufacturing solid, composite fuel bodies from one or more ground-down combustible components includes the ground-down combustible components, that partly comprise ground-down reed canary grass, being compressed to fuel bodies, whereby thermoplastic in molten form is added to the solid component forms prior to compression. The device for manufacturing fuel bodies includes a mixing zone for mixing the ground-down combustible materials that comprise the fuel body, a compression zone for compressing together the components into a fuel body, and an inlet arranged at the mixing zone for supplying the ground-down combustible material in solid form, in which a nozzle is arranged through which the thermoplastic is fed out in molten form.

Description

Method and device for manufacturing composite fuel bodies

The present invention concerns a method and a device for manufacturing composite fuel bodies such as briquettes and similar that include one or more solid combustible materials.

The recycling of different materials has gained in importance in modern society. However, it is neither possible nor suitable to re -use all materials directly in new products. A known alternative is therefore to use certain recycled or collected material to produce energy by incineration.

Collected combustible material, e.g. wood, wood fibre, rubber, plastics and other solid material, can be used with advantage during incineration because it often has a high content of energy.

It is known that recycled materials can be ground-down, for example by means of a grinding mill, before they are fed to a combustion chamber.

To increase the energy value per unit of volume, it is known to compress the material that is to be incinerated. For example, it is known to manufacture wooden briquettes by compressing wood chips. The briquette is held together by lignin, a substance found naturally in trees. Under the influence of a very high pressure, the lignin appears and binds together the wooden components in a weak manner so that they are formed into briquettes. The volume won for a specific content of energy is a major reason for using briquetting and pelleting.

A known method for manufacturing briquettes of only wooden material includes the wood being ground and then compressed to a composite briquette. Variations of this method can be found in two main groups. In the first, the briquettes are formed in a discontinuous manner, whereby the ground wood is compacted by a piston operating in a linear manner in a cylinder. In the second, the briquettes are formed in a continuous manner, whereby the ground wood is compacted by being pressed by means of a screw-feeder through a compressing nozzle for forming briquettes.

To further increase the energy content of a wooden briquette, for example, it would be desirable to mix in other components with an energy content greater than wood. One such material with a high energy content is plastic, e.g. recycled plastic.

When adding material other than wood to manufacture a briquette, the lignin does not provide sufficient adhesion to hold together a body such as a briquette.

Incinerating plastic material gives rise to by-products that do not always have a positive effect on the environment in the immediate vicinity or the surrounding nature. The objective of the present invention is to achieve a method and a device for manufacturing fuel bodies of solid material including thermoplastics as an adhesive agent and that have positive environmental effects.

This objective is achieved with a method and a device first named above and that have the features that are defined in the characteristics of the enclosed independent claims .

Embodiments of the invention are evident from the following non-independent claims.

It is desirable that the material that itself forms the briquette achieves the binding without the addition of adhesive agents. As the adhesive agent, we therefore use thermoplastic, a component that increases the energy content.

In order for the volume taken up by the thermoplastic in the briquette to be minimised, and for its potential as an adhesive agent to be realised, it should already be molten when the briquettes are compressed.

The temperatures that are required to melt thermoplastics such as polyethylene or polypropane to the extent that they are able to function as adhesives is usually in the range 200- 230 °C. However, heating the area of compression up to these temperatures is not without its problems. The thermoplastic tends to stick firmly to the compression device at the piston or at the screw conveyor. Another problem that can occur is that the wooden components begin to carbonise and risk catching fire. The carbonisation process begins at temperatures around 120°C and then increases with increased temperature.

Our invention even solves these additional problems.

Further features and advantages are evident from the following description of a non- limiting but preferred embodiment of the invention. The following description includes references to an enclosed drawing where fig. 1 schematically and in a partially exposed manner shows a perspective view of a device according to one embodiment of the present invention.

Fig. 1 shows a device for the continuous manufacture of fuel bodies in the form of briquettes from ground-down combustible material in a solid form according to one preferred embodiment of the invention.

The device includes a mixing zone for mixing the components that make up the fuel body, a compression zone for compressing together the components as well as an output zone where the formed fuel bodies exit from the compression zone. In addition, an inlet to the mixing zone is arranged for feeding the ground-down combustible material in solid form, and in this inlet, a nozzle is arranged for the thermoplastic to be fed out in liquid form.

In more detail, the device includes at least one feeding device, e.g. in the form of a conveyor 1 for feeding the solid formed components towards the input zone 2. The conveyer can be of any type at all that is suitable for feeding solid material in a ground-down form, e.g. a conveyor belt, rocking chute, gradient or a feeding device at the bottom of a container. In the example shown, the conveyor is a screw conveyor 1. The conveyor feeds the solid component forms forward in an amount that is regulated per unit of time. If precise regulation of the composition of several components in solid forms is required, it can be advantageous if an adjustable conveyor is arranged to feed each respective component.

The conveyor 1 feeds the ground-down solid material to the input zone. The input zone includes the inlet 2 to the mixing zone 3. The solid material that has been fed in is mixed in the mixing zone. In the present embodiment, the mixing zone comprises an essentially cylindrical- shaped chamber 4. A mixing screw 5 is arranged in the chamber for the stirring and axial displacement of the solid component forms that were fed into one end of the chamber through the inlet.

To improve the stirring and the mixing, projections (not shown) can be arranged along the inner walls of the chamber 4 with the task of preventing conveyed material merely sliding along the walls of the chamber and not being mixed. Parts of the solid component forms that are located closest to the walls of the chamber 4 are moved by the mixing screw towards the projection where they are forced to a stop and thus stirred. The projection can be formed as a ridge in a continuous screw-like linear form from one end of the chamber to the other, as ring- shaped ridges around the chamber, as discontinuous stirring projections along the length of the chamber, etc. A prε-requisite is, however, that the radial extension of the projection in the chamber does not hamper the screw 5. An example of a suitable radial extension of the projection in the chamber 4 is 5 - 10 mm. An example of a suitable gap between the projection and the outer radial parts of the screw is 3-10 mm. The mixing screw 5 is preferably connected to a suitable adjustable driving device such as an electric motor with an adjustable speed of revolution. The compression zone is connected to the other end of the chamber 4. The compression zone can be considered to include the end of the chamber 4 and a restricted-diameter extension of it. In the present embodiment, the restricted-diameter extension includes a compression nozzle 6. The compression nozzle has a channel 8 converging towards a tighter opening 7. The converging channel can be circular or have another cross-sectional form. It can also have differing cross-sectional forms in different positions. The opening 7 influences the form of the briquette that exits through it, and can be circular, oval, rectangular or some other suitable or desirable form. In the example shown, the converging channel is circular with a smooth change in its dimensions. A post-shaping nozzle 9 is arranged exterior to opening 7 with an internal channel whose internal cross-sectional shape closely agrees with the cross-sectional shape of the opening 7 but which then diverges to accommodate the tendency of the exiting compressed briquette to expand somewhat.

In addition, a nozzle 10 through which thermoplastic is fed out in molten form is arranged in the input zone and extending into the inlet. This feeding out preferably takes place through a spraying nozzle to achieve a distribution of the molten plastic among the solid component forms prior to them entering the mixing zone 3.

The supply of the molten thermoplastic preferably takes place continuously and from a suitable device, e.g. extrusion equipment. The extrusion equipment can advantageously be loaded with ground-down, crushed or granulated recycled thermoplastic. The extrusion equipment can be a standard kind currently available on the market or a specially designed type that comprises a part that is integrated with the other parts of the device.

The post-shaping nozzle 9 can advantageously be provided with a means of heating to enable the nozzle to be maintained at a temperature of around 80 °C or within an interval of 80°C ±5°C.

The method for manufacturing composite fuel bodies in a continuous process according to the present embodiment includes that thermoplastic is added to ground-down solid component forms such as crushed, chopped or chipped components of combustible material, preferably via a spray nozzle, prior to the components being compressed to a fuel body.

Preferably, the molten plastic is added before mixing of the solid fuel component forms takes place. The solid fuel component forms are fed to an input zone at a specified rate. The thermoplastic is fed to the input zone by means of a spray adjacent to the entry into the mixing zone in liquid form and at a specified rate.

Experiments have shown that a briquette mixture of 70 % combustible wooden material and 30 % recycled plastic, in a fraction that is representative for recycled plastic today, easily conforms with the environmental requirements for incineration in medium-sized boilers today. With regard to these discussions of mixtures, the term generally used is percentage by weight.

Normal fractions of recycled plastic are considered to contain LDPE, HDPE, ABS, PVC, EPDM, polystyrene, polypropane and polycarbonate. In a normal fraction of recycled plastic, the proportion of PVC-containing plastic is usually less than 10 % of the fraction. This should therefore be borne in mind when composing a formula, whereby the total chlorine content of the briquette should be less than 1 % .

An addition of reed canary grass to the wooden material has been shown to produce a positive environmental effect during incineration. The incineration of material mixed with plastic gives rise to the emission of organic substances (dioxins, PCB, PAH, etc.). Mixing in reed canary grass has a neutralising effect on this. Reed canary grass also helps bind chlorine and other substances that are known to be found in PVC. Reed canary grass can advantageously be included in the briquette with a percentage by weight of 0-10 % , preferably 10 % . A higher proportion has not been demonstrated to increase the positive environmental effects. Reed canary grass is a perennial grass, about two metres high with a strong, rigid stem, broad leaves and a long panicle. Reed canary grass grows wild in Sweden and is cultivated as fodder in several parts of the world. Different species of grass for use as biological fuels have been studied in field experiments since the beginning of the 1980s. Reed canary grass has provided the biggest harvests and has been the most robust and resistant of all the species tested. Thanks to its low water content, reed canary grass can be stored long-term without any great risk of mould formation or loss of substance.

The term molten plastic has been used above. This refers to the liquid phase of the material and not to its solid phase, irrespective of the viscosity.

From an environmental point of view, the proportion of plastic included in the briquette should not exceed 30 % . The larger the proportion of plastic in the briquette that is added in molten form, the more compact the briquette is, thereby further increasing its energy content in comparison to adding a portion of the plastic in solid form.

Claims

1. Method for manufacturing solid, composite fuel bodies from one or more ground-down combustible components that includes the ground-down combustible components being compressed to fuel bodies characterised in that the solid component forms comprise partly ground-down reed canary grass and that thermoplastic in molten form is added to the solid component forms prior to compression.

2. Method according to claim lcharacterised in that the solid components forms are added at a specified rate, that the molten thermoplastic is added at a specified rate, and that following mixing, the solid components forms and the thermoplastic are introduced into a compression zone for compressing into fuel bodies.

3. Method according to any of claims lto2characterised in that the proportion of thermoplastic added in molten form is in the range 10-30 percent by weight, preferably 30 percent by weight.

4. Method according to claim 3characterised in that the proportion of plastic material added is less than 30 percent by weight and that the proportion of plastic material added in solid form is less than 10 percent by weight.

5. Method according to any of the previous claims characterised in that the proportion of reed canary grass constitutes up to 1-10 percent by weight, preferably 10 percent by weight.

6. Device for manufacturing fuel bodies in a continuous process by means of the method according to claim 1 that includes a mixing zone for mixing the ground-down combustible materials that comprise the fuel body and a compression zone for compressing together the components into a fuel body characterised in that an inlet to the mixing zone is arranged for supplying the ground-down component material in solid form, and that in this inlet, a nozzle is arranged for the thermoplastic to be fed out in molten form.

7. Device according to claim όcharacterised in that the nozzle has several openings for spraying the thermoplastic fed out in molten form.

8. Device according to claims 6or7characterised in that the mixing zone comprises an essentially cylindrical-shaped housing, that an axially-operating feeding screw is arranged in the housing for mixing and feeding the material, that the said inlet is arranged at one end of the housing, and that the said compression zone is arranged at the other end of the housing.

9. Device according to claim 8characterised in that the compression zone adjoins to and forms an extension of the housing, that the compression zone has a converging cross-sectional area to achieve the said compression of the material fed to it.

10. Device according to any of the previous claims characterised in that an output nozzle is arranged as a direct extension of the compression zone with a channel for receiving a formed briquette that diverges in comparison with the opening of the compression zone, and that the output nozzle has a temperature in the range 60-90 °C, preferably 80 °C.