EP0870065A1

EP0870065A1 - A method for the pneumatic delivery of plastics-containing materials into a reaction vessel

Info

Publication number: EP0870065A1
Application number: EP95941791A
Authority: EP
Inventors: Dirk August Alois Osing
Original assignee: Heckett Multiserv PLC
Current assignee: Heckett Multiserv PLC
Priority date: 1995-12-22
Filing date: 1995-12-22
Publication date: 1998-10-14
Also published as: AU4309496A

Abstract

A method is provided to improve the pneumatic delivery of plastics-containing materials into a reaction vessel. The invention provides a method for the pneumatic delivery of plastics-containing fine-grained materials into a reaction vessel (10) which is characterized in that the plastics-containing materials are mixed before introduction into the reaction vessel with a fine-grained addition material which has at least one electrically conductive component which thereby reduces or prevents electrostatic charge build up on the plastics particles during their delivery.

Description

A METHOD FOR THE PNEUMATIC DELIVERY

OF PLASTICS-CONTAINING MATERIALS

INTO A REACTION VESSEL

This invention relates to the pneumatic delivery of plastics containing materials into a reaction vessel.

From DE-A-4104252 a method for the disposal of carbon-containing waste substances utilising their carbon content and energy content is known in which, among other things, shredder residue having a high proportion of plastics as well as waste from the production of plastics is introduced pneumatically via the tuyeres into the hearth of a metallurgical shaft furnace, which may be a blast furnace for making pig iron. The waste substances are introduced into the hot blast currents supplied to the individual tuyeres and blown together with the blast into the hearth of the blast furnace.

Further, from US-A-4,266,968, a method is also known for the continuous injection of fine¬ grained lignite or brown coal into the hearth of a blast furnace through the tuyeres thereof.

The injection of fine-grained plastics or of coarse plastics mixtures, however, can cause problems because the plastics particles become electrostatically charged in the course of transport through the delivery pipes to the respective reaction vessel with the result that the plastics particles may adhere to the wall of the delivery pipe to the reaction vessel. In severe cases the delivery pipe can suffer within a short time a considerable reduction of its free cross-section and may become completely blocked. Owing to the building-up of the plastics particles on the walls of the delivery pipe, it becomes more difficult to convey and provide requisite amounts of the plastics particles. The build-up takes place more particularly in the curved regions of the delivery pipes and at transition and connection regions between two consecutive pipes or flexible tubes.

Further difficulties may be encountered, particularly when the reaction vessel is operated at high temperatures such as is the case, e.g. with a blast furnace. These additional difficulties arise because the thermoplastic particles adhering to the wall of the delivery pipe soften and become sticky under the action of the heat radiating from the reaction vessel. The softened plastics particles can bake on to the wall of the pipes and blocking of the delivery pipes takes place even more quickly. Moreover, it has been found that the depositing of electrostatically charged plastics particles may cause damage to the delivery pipes which under certain circumstances may even lead to their destruction.

The invention starts from a method according to the preamble of Claim 1. It is based on the object of developing a method for the pneumatic delivery of fine-grained or coarse electrostatically chargeable materials, e.g. plastics, which method at least largely reduces the aforementioned difficulties without thereby causing further complication so that, if desirable, it can be applied to already existing equipment without great extra expense.

Accordingly the invention provides a method as defined in Claim 1 below. Thus the invention provides that the electrostatically chargeable materials are blown in mixed with at least one additional fine-grained material component whereby the drawbacks, more particularly the build-up of material particles on the wall of pipes or the like under the action of electrostatic charges, no longer occur or only to an extent which does not impair the operation. The addition materials may also be waste substances which must be "compatible" with the reactions which run their course if necessary in the reaction vessel in such a manner that they do not have a detrimental affect on the course of the reactions and, e.g. do not lead to the presence of undesired constituents in the blast product to be made in the blast furnace or another reaction vessel. In the event of the injection of the plastics particles into the hearth of a blast furnace for making pig iron, Fe-bearing rolling mill scale slurry for instance may be used as at least one addition component. Such slurry may be used after preparation according to the method described in EP-OS 0499779. However, other addition materials may also be used which reduce the electrostatic charges induced on the plastics particles. It may be, for example, iron ore, or sponge iron, more particularly ultra-fine-grained sponge iron, which is also available as a waste product. Graphite, coke or coal may also be used under certain circumstances as addition materials causing the desired effect.

Which addition materials are suitable and in which quantity they must be mixed with the plastics materials in order to achieve the desired effect can be determined by simple tests. In this respect the grain size distribution may also play a role because the increase of the electric conductivity of the system formed by the mix is also dependent on the distribution of the conducting materials in the mix. In the case of harder, more particularly metal, addition materials will also contribute to prevent the build-up or cake-on of plastics particles.

In-depth tests more particularly with the fine grained or coarse plastics have revealed that, by means of admixing corresponding amounts of prepared rolling mill scale slurry, an injection operation via the tuyeres can be maintained for an almost unlimited time, wherein the pneumatically conveyed material is dosable as a function, e.g. of the requirements of the reactions taking place in the reaction vessel and shows no tendency at all to build-up or cake-on. More particularly, in contrast to the delivery of plastics material alone, delivery of the mixture according to the present invention provides satisfactory delivery performances. This may also be attributable to the fact that rolling mill scale slurry and other Fe-containing materials are considerably heavier than the plastics materials and thus during pneumatic conveying form a material flow which carries along with it the plastics particles which exhibit a considerably greater specific volume. This effect also contributes to the good regulability and proportionability of the material flow. It is expected, moreover, that rolling mill scale slurry - and other Fe-containing materials, based on their considerably greater thermal conductivity in comparison to plastics, make a considerable contribution to the cooling of the supply pipe when the latter is subject to the action of heat from the reaction vessel.

Plastics waste from industry and, which may be particularly important, the usual plastics constituents of domestic refuse, may also be injected into a reaction vessel in the described manner. More particularly, the waste from domestic refuse may be mixtures of plastics, which contain duroplasts and thermoplasts and in addition also those plastics, e.g. PVC, which in the presence of unfavourable conditions lead to the formation of dioxins and furnaces owing to their Cl content. When introducing the plastics into metallurgical furnaces, such as, e.g. a blast furnace, one can reckon that due to the operating conditions, especially the temperature, of such a furnace all the plastics under consideration can be injected without having to fear the formation of undesired or even toxic substances which would be discharged with the waste gas, e.g. the flue gas of a blast furnace.

The size of the particles of the mixture depends on the one hand on the requirements of the pneumatic conveying system and on the other hand also on the necessity for a sufficiently fine distribution of the addition material to reduce the electrostatic charge sufficiently, in order to attain the desired effect. Thus the plastics particles may exhibit a larger grain size than the particles of the addition material, e.g. the rolling mill scale. Generally, the plastics particles have a grain size of smaller than 8 mm, more particularly smaller than 6 mm.

The plastics mixture will generally also contain rubber and textile constituents and also metal particles, the latter admittedly to a more negligible extent. The maximum grain size of this lightweight fraction is generally 6 mm.

Instead of rolling mill scale slurry, other metal or metal-containing waste substances may also be used, for instance metal-containing blast furnace gas dusts so long as they can reduce or prevent the electrostatic charging of the plastics particles. Ores may also be considered. These predominantly metal substances preventing or at least noticeably reducing the electrostatic charge are generally present in very fine granulation, e.g. below 0.5 mm or as dust, because they obtain their effect, at least to a large part, in that they cover the surface of the plastics particles at least partly and so increase the electric conductivity of the surface. Should the injection of additional substances or mixtures into the reaction vessel be desired or necessary, these substances or mixtures can be added to the delivery stream consisting of plastics particles and those materials which at least reduce the electrostatic charge of the plastics particles.

The drawings show in diagrammatic form one possible arrangement of equipment for the pneumatic delivery and injection of plastics-containing fine grained materials according to the invention.

Figure 1 shows an apparatus for feeding the mixture into a blast furnace; and

Figure 2 shows the connection of the apparatus to the blast furnace on a larger scale.

The apparatus is provided with two bins I, II. Bin I contains a fine-grained material consisting at least predominantly of fine grained or coarse plastics, Bin II contains a mixture which contains rolling mill scale slurry and has been obtained by treating the latter by the method according to EP-0499799 A1. The two bins I and II are located adjacent to a delivery and proportioning screw (5) which mixes the components supplied from the two bins in the respectively required amounts and, via a pipe (6), leads to an intermediate tank (8) beyond which is located a lock-gate-type chamber (10). Beyond the latter is positioned a pressure vessel (16), and a valve (15) or the like is provided between lock- gate-type chamber (10) and pressure vessel (16). In the lower region of the pressure tank (16) there is a perforated base (20), from below which an optionally heated gas or gas mixture, preferably air, is supplied through a delivery pipe (22) and causes the formation of a fluidised bed above the perforated base, this bed consisting of the materials which have been fed in from the bins I and II. From this fluidised bed above the perforated base (20) in the tank (16) which is under excess pressure, the mixture is delivered pneumatically through the fluidising medium via the pipe (19) into the hearth (24) of a blast furnace. The hearth (24) is provided in the usual manner with tuyeres (28) distributed over the circumference, through which hot gas is blown into the hearth (24). This hot blast, generally pre-heated to a temperature of 900-1000°C, is supplied to the tuyeres through a closed-circuit pipe line (30) from which branch pipes (32) lead out to the individual tuyeres (28). As shown more particularly in Figure 2, the pipe (19) coming from the pressure vessel (16) continues into a lance-like tube (34) which penetrates the wall of the tuyere (28) or the delivery pipe itself and ends in the direction of flow (36) just before the hearth-side boundary of the tuyere (28).

The length of standard tuyeres is 350-550 mm. The inside diameter may amount to perhaps 150 mm. The position (38) at which the lance-tyre tube (34) enters the tuyere may be situated perhaps 350 mm from the hearth-side end of the tuyere (28). The angle of entry of the tube (34) into the tuyere is 15° to 24°. The hearth-side end of the lance-like tube (34) is situated about 250 mm from the hearth-side end of the pertaining tuyere. The example shown in the drawings corresponds to the standard arrangements and models of blast furnaces for the production of pig iron, so that this kind of injection equipment is already available for injection of coal, ore or the like. Independently of the nature and the material used for the equipment no build-up or bake-on of plastics (which is considerably detrimental to the operation of the equipment) takes place on the inside wall particularly of the delivery pipe (19) and the lance-like tube (34). In the drawings only one of the tuyeres (28) is fitted with a lance-type tube (34) for feeding the mixture. It is self-evident that also a plurality, and if desired, all tuyeres may be provided with lance-like tubes for the injection of the solid material mixture. In this respect a special delivery pipe from the pressure tank (16) may be provided for every tuyere (28) having a lance-like tube (34). However, it is also possible to provide a common delivery pipe from the pressure tank up to the vicinity of the hearth (24) and to have branch pipes there from this common delivery pipe to the individual lance-shaped tubes.

Claims

1. A method for the pneumatic delivery of plastics-containing fine grained materials, which are electrostatically chargeable, into a reaction vessel, characterised in that the plastics-containing materials are mixed before introduction into the reaction vessel with a fine-grained addition material which has at least one electrically conductive component which thereby reduces or prevents electrostatic charge build up on the plastics particles during their delivery.

2. A method according to Claim 1 , characterised in that the plastics-containing materials comprise waste materials.

3. A method according to Claim 1 or 2, characterised in that the plastics-containing materials embody industrial waste.

4. A method according to Claim 1 or 2, characterised in that the plastics-containing materials embody plastics waste from domestic refuse.

5. a method according to one of the preceding Claims, characterised in that the addition materials to reduce or prevent the electrostatic charge embody at least one metal component.

6. A method according to Claim 5, characterised in that the addition materials embody rolling mill scale slurry.

7. A method according to claim 5, characterised in that the addition materials embody metal dusts.

8. A method according to Claim 5, characterised in that the addition materials to reduce or prevent the electrostatic charge are fine ores, which have a sufficient electric conductivity.

9. A method according to any preceding Claim, characterised in that the addition material contains graphite, coke and/or coal, which have a sufficient electric conductivity.

10. A method according to any preceding Claim, characterised in that the plastics- containing materials and the addition materials are mixed together before they are delivered pneumatically into the reaction vessel.

1 1. A method according to Claim 10, characterised in that the plastics-containing materials and the addition materials are added separately into a pipe inside which the pneumatic delivery takes place, and are mixed together in the pipe by means of the carrier medium.

12. A method according to any preceding Claim, characterised in that the plastics- containing materials have a maximum grain size of 8 mm.

13. A method according to Claim 13, characterised in that the addition material to reduce or prevent build up of electrostatic charge on the plastics particles has a grain size of at least predominantly 0 - 1 mm.

14. A method according to any preceding Claim, characterised in that the amount of the addition material admixed to the plastics-containing material makes up 30% by weight of the plastics-containing material.