WO1999051320A1

WO1999051320A1 - Cyclonic effect pre-abatement chamber to process fumes in industrial plants

Info

Publication number: WO1999051320A1
Application number: PCT/IB1999/000580
Authority: WO
Inventors: Gioacchino Nardin; Alessandro Rocco; Mario Floreani
Original assignee: Universita degli Studi di Udine
Current assignee: Universita degli Studi di Udine
Priority date: 1998-04-07
Filing date: 1999-04-02
Publication date: 1999-10-14
Anticipated expiration: 2000-10-07
Also published as: ITUD980056A1; IT1299770B1; ITUD980056A0; AU2849899A

Abstract

Cyclonic effect pre-abatement chamber to process fumes from industrial plants, the chamber being arranged downstream of said plants and upstream of purification, final filtering and discharge devices, the pre-abatement chamber being equipped with at least an inlet aperture and at least an outlet aperture, and internally defining a transit and expansion volume for the fumes, wherein the inlet aperture (21) and the outlet aperture (20) are arranged respectively tangential and axial with respect to the transit and expansion volume (19), and wherein the transit and expansion volume (19) defines a substantially spiral path for the fumes (24) between the inlet aperture (21) and the outlet aperture (20) suitable to generate a rotation of the fumes (24) of less than 360°.

Description

"CYCLONIC EFFECT PRE-ABATEMENT CHAMBER TO PROCESS FUMES IN

INDUSTRIAL PLANTS" * * * * *

FIELD OF THE INVENTION This invention concerns a cyclonic effect pre-abatement chamber to process fumes in industrial plants as set forth in the main claim.

The invention is used in industry to achieve the preliminary processing of gassy currents characterised by high temperature and large quantities of solid polluting material in suspension therein, before they are sent to energy recovery devices and/or devices for final filtering, purification and discharge into the atmosphere.

The invention is applied particularly, but not exclusively, in the processing of fumes discharged from electric arc furnaces used in the steel industry and from the incinerator furnaces used in waste disposal, although the application can substantially be extended to every type of processing of industrial fumes where it is necessary to perform a pre-abatement of the powders upstream of the final filtering.

The pre-abatement of the powders achieved by the chamber according to the invention is characterised in that it is obtained with very limited losses of load in the gassy current which contains the powders which have to be abated.

BACKGROUND OF THE INVENTION In numerous industrial fields the processing of high temperature gassy currents is a particular problem when the currents are characterised by the presence of suspended particles which have to be separated as much as possible from the gassy current before they pass into energy recovery systems or final filtering systems which precede discharge into the atmosphere. For it is well-known that there are extremely restrictive legislative norms on the maximum limits allowed of polluting substances in the gassy currents produced by industrial plants before they are sent to the chimney and discharged. The characteristics of the suspended particles are very variable and depend on the thermo-dynamic conditions and on the specific production process which generate them.

At present, the gassy currents or fumes are conveyed through energy recovery devices or final filtering and purification devices, but their efficiency is adversely affected by the presence of high quantities of these suspended particles.

Moreover, the suspended particles, which can also be quite large, may reach these devices still in an incandescent state, causing serious damage thereto, particularly in the case of sleeve-type filters.

The high velocity of the fumes and the presence of large quantities of suspended particles also leads to premature wear of the components in these final filtering and purification devices, or alternatively it becomes necessary to use increased thicknesses, special linings or materials, with consequent additional costs .

These devices therefore always work under extreme conditions and need frequent cleaning, maintenance and/or replacements, which entails prolonged interruptions in the production processes which generate the fumes .

In order to at least partly eliminate the particles suspended in the combustion products, and to complete the processes of thermo-destruction of the pollutants, various solutions have been proposed, such as decelerating chambers, inverted flow chambers and barrier chambers; however, these have all proved to be not very functional and/or relatively limited in their collection capacity. These solutions, moreover, cause enormous load losses, which entails a high absorption on the part of the ventilators which take in the fumes and therefore a very considerable increase in the energy consumption of the plant .

If this may not be a very serious problem in small plants, it is a crucial problem in large steel plants or in large incinerators, causing a huge economic burden due to the consumption of electric energy. The present Applicant has devised and embodied this invention to overcome these shortcomings and to obtain further advantages as will be shown hereafter.

SUMMARY OF THE INVENTION The invention is set forth and characterised in the main claim, while the dependent claims describe other characteristics of the main embodiment.

The purpose of the invention is to achieve a pre-abatement chamber to process fumes generated by an industrial plant, the chamber being characterised in that it has a high ratio between its efficiency in powder abatement and low load losses generated on the gassy current.

In other words, the invention proposes to obtain a pre- abatement of the polluting substances transported by the processing fumes wherein it will be possible to obtain a good efficiency in separating the substances, yet still maintain low load losses in the gassy flow in transit.

The reduced load losses caused by the passage of the gassy current in the pre-abatement chamber according to the invention determine a very limited absorption of power by the ventilators; the greater the gassy currents to be purified, the more the absorption of power affects the overall consumption of electric energy.

Another purpose of the invention is to reduce wear and the frequency of maintenance interventions on the devices, reducing the quantity of polluting particles suspended in the gassy currents discharged from the industrial plants before the currents reach the energy recovery devices or the final filtering and purification devices.

A further economic advantage of using the pre-abatement chamber according to the invention is obtained when it is used in plant situations where it is necessary to abate high concentrations of polluting substances such as dioxins, furans or substances containing chlorine or fluoride, the concentration of which must be reduced to very limited values before they are discharged into the atmosphere, as established by legislation.

In this case, in fact, if they are abated in the chamber according to the invention, by reducing the concentration of such polluting substances, it is possible to considerably reduce the quantity of extremely expensive neutralising chemical agents which are introduced into the fume intake circuit before the final filtering. It may therefore be economic to use inexpensive adsorbent substances (for example, lime) to achieve a pre-abatement of the polluting substance in question, then pre-abatement with the chamber according to the invention and finally abate the polluting substance to within the legal limits downstream of the chamber according to the invention using the more expensive specific adsorbent substances (for example bicarbonate of soda) .

In this last step it is obvious that the quantities of high cost adsorbent substances which will have to be used will be relatively small, given the reduced residual quantity of polluting substances which have to be abated.

The pre-abatement chamber according to the invention is installed in a position of close proximity with the outlet of the fumes from the industrial plant, so that fumes circulate inside the chamber at a very high temperature, as much as 900°C and more, at least in the case of steel plants . The pre-abatement chamber according to the invention consists in its essential parts of a pair of lateral covers, at least a shaped outer wall and at least a shaped inner wall which, once assembled, define an inner transit and expansion volume, communicating with the outside through at least an inlet aperture and at least an outlet aperture.

The inlet and outlet apertures are connected respectively to the outlet of the industrial plant which emits the fumes and to the inlet of any energy recovery device, or final filter and purification device. According to the invention, the inlet and outlet apertures are arranged respectively tangential and axial to the transit and expansion volume, and the shaped inner wall acts as a deflector element for the entering fumes, defining an outlet direction substantially orthogonal to the inlet direction.

The shaped inner wall, in cooperation with the shaped outer wall, defines a desired semi-cyclonic path for the gassy current, from inlet to outlet, which encourages a high efficiency of abatement, separation and decantation of the solid polluting particles, such as powders, ashes and slag, suspended and transported in air in the current of gas .

The solid polluting particles when separated settle on the bottom of the pre-abatement chamber in at least a collection and discharge zone, for example conformed as a hopper. According to one embodiment of the invention, the shaped inner wall is arranged longitudinally with respect to the lateral covers for the whole distance between them, substantially orthogonal thereto and at least partly parallel to the outer wall.

According to the invention, the cyclonic path of the fumes has a substantially horizontal, sub-horizontal or vertical development, and imparts to the gassy current, from inlet to outlet, a rotation of less than 360°, advantageously in the order of about 270°.

Using a curved path covering an angle of about 270° gives a double advantage:

- on the one hand, it allows to technologically achieve the cyclonic effect with low load losses, in that it prevents inversions of direction and continuous rotations of the gassy flow; on the other hand, it ensures high efficiency of abatement, since it has been found that an angle of 270° corresponds substantially to the bend of the efficiency/ limit angle curve relative to a cyclone abatement device.

According to a variant, there are several pre-abatement chambers according to the invention arranged in series; this allows to increase the effect of abating and decanting the solid polluting particles

According to another variant, the pre-abatement chamber cooperates with at least one burner or air injector so as to increase the combustion of the residual volatile pollutants and the noxious compounds contained in the gassy current . BRIEF DESCRIPTION OF THE DRAWINGS

The attached Figures are given as a non-restrictive example and show a preferential embodiment of the invention wherein:

Fig. 1 is a diagram of a pre-abatement chamber associated with the hole to discharge fumes of an electric arc furnace; Fig. 2 is a three-dimensional view of the pre-abatement chamber shown in Fig. 1; Fig. 3 is a cross section of Fig. 2; Fig. 4 is an exploded view of Fig. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Fig. 1 shows an example of an electric arc melting furnace 10, which has a roof 10a with a hole 11, known as the fourth hole, through which the fumes produced during the melting cycles are discharged.

It is obvious that the invention can be applied, not only to the melting furnace 10, but also to an incinerator or any other industrial plant which produces fumes containing substances which have to be filtered and purified before being discharged into the atmosphere.

The fumes discharged from the fourth hole 11 are conveyed, through a pipe 12 associated with an inlet union 26, directly inside the pre-abatement chamber 13 according to the invention, in which the fumes in transit reach temperatures of 900°C and more.

The chamber 13 in this case is arranged horizontal, but it could be arranged at an angle with respect to the base on which the furnace 10 rests.

The pre-abatement chamber 13 is associated at outlet, by means of a union 22, to a pipe 14, indicated by a line of dashes, connected downstream with a purification and final filtering device and a chimney to expel the fumes into the atmosphere; these devices are not shown in the drawings.

The pipe 14 could also convey the fumes to an energy recovery device which uses the thermal energy transported by the fumes .

The pre-abatement chamber 13 consists (Figs. 2 and 4), in its essential parts, of a first lateral cover 15, a second lateral cover 16 parallel and opposite the first cover 15, a shaped outer wall 17, substantially quadrilateral and closed at the front by the said covers 15 and 16, and an inner wall 18 which is also shaped.

The elements 15, 16, 17 and 18 define an inner volume 19 for the fumes 24 emerging from the furnace 10 to pass through and expand; the inner volume 19 communicates with the outside through an inlet aperture 21 and an outlet aperture 20.

The inlet aperture 21 is defined by the shaped and parallel end segments 17a and 17b of the outer side wall 17; it is connected with the fourth hole 11 of the furnace 10 by means of the pipe 12 and a union 26, and defines a substantially tangential inlet direction for the fumes 24 with respect to the transit and expansion volume 19.

The outlet aperture 20 is made on the first cover 15 and is directly connected, by means of the union 22, to the subsequent devices for the final filtering and discharge of the fumes .

The outlet aperture 20 defines a substantially axial outlet direction for the fumes 24 with respect to the transit and expansion volume 19, and substantially orthogonal with respect to the inlet direction.

The shaped inner wall 18, arranged inside the transit and expansion volume 19, consists of a first, substantially rectilinear segment 18a which extends towards the inlet aperture 21, and a second, substantially curved segment 18b, with a radius substantially mating with the outlet aperture 20.

The shaped inner wall 18 extends longitudinally between the first cover 15 and the second cover 16, and is substantially orthogonal thereto, covering the entire distance between them.

The first, rectilinear segment 18a of the shaped inner wall 18 joins the end 17b of the outer lateral wall 17

(Figs. 3 and 5) and defines, together with the end 17a, a rectilinear inlet segment for the fumes 24 into the pre- abatement chamber 13.

The second, curved segment 18b of the inner wall 18 substantially couples with the outlet aperture 20 of the fumes 24, defining with respect thereto a transit space 23 (Fig. 3) through which the fumes are directed towards the outlet 20 with a last, substantially rectilinear outlet segment; here the fumes travel in a direction substantially orthogonal to the inlet direction. The fumes 24 are induced by the curved conformation of the inner wall 18 to follow a spiral path around the chamber 13, which achieves an angle of rotation which is less than 360° until the outlet aperture 20, first on the outside around the curved segment 18b of the shaped inner wall 18, and then on the inside of said segment 18b, passing through the transit space 23.

To be more exact, according to the invention the curved segment 18b defines an angle of around 270°, in order to achieve an optimum ratio between the abatement of the polluting powders and losses in load of the gassy flow, which losses are directly correlated to the absorption of power on the part of the ventilators of the intake plant.

The present Applicant has in fact found that with every further cyclonic circulation of the flow, the efficiency of abatement does not significantly increase, while, on the contrary, the load losses become higher and higher, particularly in the case of large quantities of fumes circulating through the pre-abatement chamber.

The semi-cyclonic development of the fumes 24 inside the chamber 13 induces a high level of turbulence in the fumes 24, subjecting the solid particles suspended therein to a high centrifugal force which separates them and decants them from the gassy current, and makes them precipitate in correspondence with the bottom of the chamber 13.

The second cover 16 has a substantially central hole 27 to discharge the abated powders; it can be associated to a removable container 25, for example of the hopper type. The semi-cyclonic configuration of the transit and expansion volume 19 can also encourage the completion of post-combustion reactions, which can be intensified by providing burners or injectors (not shown here) on the walls of the chamber 13. As a result of separating the solid components transported by the gassy currents in an efficient and substantial manner, there is a reduced deposit of powders and ashes on the energy recovery and final filtering devices located downstream, which means they are subjected to less wear and maintain their high performance for a longer period.

Moreover, there are lesser concentrations of unwanted particles, such as carbon compounds, copper chloride, etc., which are particularly harmful because of their potential to act as catalysts in reactions to form dioxins and furans in the components downstream from the pre-abatement chamber 13. A further advantage is that a first separation occurs of the particles containing heavy metals, which is completed in abatement plants located downstream of the energy recovery section. The high level of turbulence obtained inside the pre- abatement chamber 13 also allows to obtain further improvements in the abatement of pollutant emissions because it achieves the practically complete destruction of the poly-cyclic aromatic hydrocarbons, and significantly reduces the unburned carbon fractions, which are potential catalysts in reforming reactions of dioxins and furans.

Claims

1 - Cyclonic effect pre-abatement chamber to process fumes from industrial plants such as electric arc furnaces, incinerator plants or similar, the chamber being arranged downstream of said plants and upstream of purification, final filtering and discharge devices, the pre-abatement chamber being equipped with at least an inlet aperture and at least an outlet aperture, and internally defining a transit and expansion volume for the fumes, the chamber being characterised in that the inlet aperture (21) and the outlet aperture (20) are arranged respectively tangential and axial with respect to the transit and expansion volume (19), and in that the transit and expansion volume (19) defines a substantially spiral path for the fumes (24) between the inlet aperture (21) and the outlet aperture (20) suitable to generate a rotation of the fumes (24) of less than 360°.

2 - Pre-abatement chamber as in Claim 1, characterised in that the substantially spiral path covers an angle of around 270° between the inlet aperture (21) and the outlet aperture (20) .

3 - Pre-abatement chamber as in Claim 1 or 2 , characterised in that it comprises a pair of parallel and opposite lateral covers (15, 16), a substantially quadrilateral shaped outer wall (17), the ends (17a, 17b) of which define the inlet aperture (21) and a shaped inner wall (18) which functions as a deflector for the fumes (24) entering the pre-abatement chamber ( 13 ) .

4 - Pre-abatement chamber as in Claim 3, characterised in that the shaped inner wall (18) has at least a first, rectilinear segment (18a) located in co-operation with the ends (17a, 17b) of the outer wall to define a substantially rectilinear segment connected to the inlet aperture (21), and at least a second, curved segment (18b) functioning as a deflector, with a radius substantially mating with the outlet aperture (20) , suitable to define the spiral path of the fumes (24) between the inlet aperture (21) and the outlet aperture (20) .

5 - Pre-abatement chamber as in Claim 3 , characterised in that a first lateral cover (15) is suitable to define the axial outlet aperture (20) of the fumes from the pre- abatement chamber (13) and is suitable to be associated with a pipe (14) connected downstream with a purification and final filtering device.

6 - Pre-abatement chamber as in Claim 3, characterised in that a second lateral cover (16) is suitable to define a substantially central hole (27) to discharge the powders separated from the fumes (24) which make up the gassy current .

7 - Pre-abatement chamber as in Claim 6, characterised in that the hole (27) is suitable to cooperate with means to collect, contain and discharge the powders. 8 - Pre-abatement chamber as in Claim 1, characterised in that the inlet aperture (21) is connected to the fourth hole (11) of the furnace (10) by means of a pipe (12) and a union (26) . 9 - Pre-abatement chamber as in Claim 1, characterised in that the outlet aperture (20) is connected to the pipe (14) by means of a union (22) .