Title of Invention

PERMEABILITY BARS WITH SELF-CLEANING ARRANGEMENT

Abstract

A self-cleaning device for clearing permeability bars of a continuous sintering machine comprising a set of cleaning fingers separately supported by a frame, said set of cleaning fingers being slidably operable over said permeability bars for cleaning the bars by scraping material sticking to the bars characterized in that the said device is operated by manually or hydraulic auto mechanism at a certain interval of time.

Full Text

FIELD OF APPLICATION The present invention relates generally to a self-cleaning device for cleaning permeability bars, and in particular to a self-cleaning arrangement used for making iron ore sinter in steel plants producing pig iron through blast furnace and sinter route. BACKGROUND OF THE INVENTION During the process of mining, lot of fine iron ore is generated at mines. However, these fines cannot be fed to a blast furnace as such to convert them into pig iron. Hence the need of agglomerating these fines into a lump is necessitated. Methods of agglomerating iron ores and iron containing waste products have been under consideration since the end of nineteenth century. The developments of these processes, however, were accelerated during the second world war. The various methods of agglomeration are: a) Briquetting b) Nodulizing (rotary kiln sintering) c) Vacuum extrusion d) Sintering (grate sintering) e) Pelletizinq Of the above methods, the last two are predominantly used for iron ore fines. Considering the fine ore characteristics, under Indian condition, sintering is more prevalent compared to pelletizing. The sintering process consists of mixing moist iron-ore fines and, other fine materials (e.g. fluxes and steel plant wastes) with solid fuel, normally coke breeze, and loading the mix on to a permeable grate. The upper surface is raised to a high temperature by oil or gas burners and air is sucked downwards through the grate. After a short ignition period, the top surface generates sufficient heat by burning of solid fuel (coke breeze) and a narrow combustion zone is formed which moves downwards under the influence of suction through the grate. When the combustion zone reaches the base of the sinter mix, the process is complete. The sinter cake, so formed is then cooled and sized for use. Sintering is a down-draught process where air carries the heat and also supplies the oxygen necessary for combustion of solid fuel present in it. Research work carried out by many, especially those of EW Voice and R Wild are considered to be fundamental for sintering process. Their work has shown that the rate determining step is the volume of air passing through a sinter bed which allows the heat transfer between various layers present within. The raw material used for sintering are ore fines, fluxes (crushed limestone, pyroxenite), solid wastes, coke breeze, lime fines, sinter return fines. All these materials are taken in a desired proportion and mixed in a mixing drum, where controlled water addition is done. The green mix so prepared is taken in the surge hopper positioned just above the sinter strand. Before laying the green mix, first a thin layer of sinter (15-25 mm size), called hearth layer is spread on the sinter strand. The aim of loading the strand with green mix is to lay down the material evenly across the width of the machine, typically in the range between 2.5 m and 3 m) with minimum compacting. This is accomplished by the use of drum feeder or feed roll. Use of segregation pad at the charging station also reduces the height of free fall and reduces velocity of falling stream of material. Permeability bars consist of a set of static strips of metal inserted within the green mix bed at the charging station. The permeability bars in a sinter machine enhance the permeability of green mix charged on to the sinter strand. Use of permeability bar further reduces the compactness of the material charged onto the strand. The practice of using permeability bar is now 15 years old. The comb like structure inserted inside the green mix bed creates certain void which is in turn filled up by re-adjusting of material when it passes under the bed height leveler plate. Thus the permeability of sinter bed really determines the rate of sintering. Realising this a lot of developments have taken shape in the charging station of a sinter machine. One of these is the 'permeability bar'. Permeability of sinter bed is measured in Japanese permeability unit (JPU). The formula for calculating sinter bed permeability is: Where, WG Volume = waste gas volume in Nm3 / min H = bed height in mm P = suction in mm water column This formula is used to calculate the permeability of the sintering plant using on-line data. The permeability value normally lies between 30-40 JPU (Japanese permeability unit). The permeability bars are installed in sinter strands of sinter plants. Although they act in improving the bed permeability to a great extent, the inherent shortcoming in the existing permeability bars cause green mix getting deposited on them in no time, making 'swollen fingers'. These in turn lead to forming unnecessary voids at the charging station. The difficulty associated with these are two-fold: It creates differential permeability across the width of the bed, and it forms rat-holes on the sinter bed. This results in poor sinter quality and loss of production. There was therefore, a need for overcoming these difficulties. SUMMARY OF THE INVENTION The main object of the present invention therefore, is to provide a new attachment for the permeability bar with an automatic cleaning arrangement which removes any deposit forming on the permeability bar fingers. Another object of the present invention is to improve the performance of the permeability bars and increase their life. Yet another object of the present invention is to improve the sinter quality by providing uniform sinter mix on the strand. These and other objects of the invention are achieved by providing a set of cleaning fingers, one for each permeability bar. These cleaning fingers can be separately supported by the frame and can be slided over the permeability bars for cleaning by scraping of materials from the permeability bars. Thus the present invention provides a self-cleaning device for cleaning permeability bars of a continuous sintering machine comprising a set of clearing fingers separately supported by a frame, said set of cleaning fingers being slidably operable over said permeability bars for cleaning the bars by scraping material sticking to the bars. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The functioning of the device is illustrated in Figures 2 to 5 of the accompanying drawings. Fig. 1 shows an arrangement of permeability bars. Fig. 2 shows a schematic flow diagram of a sintering plant. Fig. 3 shows the cleaning device in idle position. Fig. 4 shows the device in cleaning position. Fig. 5 shows the general arrangement of the permeability bars with cleaning fingers. DETAILED DESCRIPTION Permeability bars consisting of a set of static strips of metal inserted within the green mix bed at the charging station is shown in Figure 1. The essential feature of Dwight-Lloyd sinter machine is a moving strand, which is made up of a series of pellets (wheeled cars) with a permeable grate and side wall. The pellets are filled with green sinter mix (also called the green mix), passed under an ignition hood, subjected to down-draught suction. The sintering process is completed before the moving grates reach the discharge end, where they are tipped and returned to the charging position. Therefore, like an endless chain, the pellets move and carry out sintering as shown in the flow diagram of Figure 2. The charging station consist of a surge hopper for green mix, feed roll, etc. Permeability bar is installed under the surge hopper. The green mix, which is fed to the sinter strand contains 6-7% moisture and therefore, is sticky in nature. Usually, the deposition on the permeability bars starts from the top. It gradually grows into a bigger lump. As the green sinter mix also contains lime fines, it makes the build-up strong enough to get dislodged by itself. The permeability bars remain submerged within a pile of material, which makes it impossible to approach while the sinter machine is in operation. The cleaning device of the present invention shown in Figure 3 makes it possible to clean the permeability bars 1 at regular interval in running condition of the sinter machine. A set of cleaning fingers 2, one for each permeability bar 1, is separately supported by the frame. The cleaning fingers 2 would normally remain outside the green mix pile. After a fixed interval, they would be pushed forward either manually by an operating lever 3 of mechanically, by a hydraulic arrangement (not shown) over the permeability bars 1. The cleaning fingers 2 have a sharpened flaps over them. While sliding over the permeability bars 1, these cleaning fingers 2 do the necessary scraping of material. The cutting flap also acts as guide and does not allow the moving fingers to deviate. Figure 4 shows the cleaning fingers 2 in advanced position. The cleaning fingers 2 are quickly retracted to its idle position, ready for the next stroke. The mechanism ensures that the permeability bar 1 always remain clean and therefore enhances permeability of the sinter mix on sinter strand. Figure 5 shows a general arrangement for the permeability bars with cleaning fingers of the present invention. It is recommended to connect operating mechanism with a hydraulic cylinder. The timing for auto operation may be set at 15 minutes interval for best results. The cleaning device of the present invention provides a very simple solution to a difficult problem. Due to the position of the permeability bar as shown in Fig. 1, it is very difficult, if not impossible, to clean them in running condition of the sinter machine. Whereas, the design of the present invention is capable of easily removing any deposit as may be forming over the permeability bars (strips) in running condition of the machine. Depending on the requirement and material type, it may be operated manually using a lever. Better option would be to mechanise the cleaning arrangement using hydraulic, pneumatic or even electrical actuators. The benefits envisaged from the device of the present invention are: 1). No deposit on the bars 2). Longer life of the permeability bars 3). Uniform bed permeability across the width of a sinter strand. 4). Improved productivity 5). Improved and consistent quality parameters of sinter produced, i.e. a) Higher Tumbler Index b) Higher Cumulative + 10mm of sinter, etc. WE CLAIM 1. A self-cleaning device for clearing permeability bars of a continuous sintering machine comprising a set of cleaning fingers separately supported by a frame, said set of cleaning fingers being slidably operable over said permeability bars for cleaning the bars by scraping material sticking to the bars. Characterized in that the said device is operated by manually or hydraulic auto mechanism at a certain interval of time. 2. The self cleaning device as claimed in claim 1, wherein said set of cleaning fingers in normal position remain outside the green mix of the sinter. 3. The self-cleaning device as claimed in claims 1 or 2, wherein said cleaning fingers are each provided with a sharpened cutting flap over them. 4. The self-cleaning device as claimed in claim 3, wherein said cutting flaps also act as guides for the fingers so that the moving fingers do not deviate. 5. The self-cleaning device as claimed in claim 1, wherein said set of cleaning fingers can be pushed forward manually by using an operating lever. 6. The self-cleaning device as claimed in claim 1, wherein said set of cleaning fingers can be pushed forward mechanically using a hydraulic operating mechanism. 7. The self-cleaning device as claimed in claim 5, wherein said hydraulic operating mechanism is provided with hydraulic cylinder with a timer for operation at regular time intervals automatically. 8. The self-cleaning device as claimed in claim 6, wherein the timer for automatic operation of the hydraulic operating mechanism is set for 15 minutes interval. 9. A self-cleaning device for clearing permeability bars of a continuous sintering machine substantially as herein described and illustrated in the accompanying drawings. A self-cleaning device for clearing permeability bars of a continuous sintering machine comprising a set of cleaning fingers separately supported by a frame, said set of cleaning fingers being slidably operable over said permeability bars for cleaning the bars by scraping material sticking to the bars characterized in that the said device is operated by manually or hydraulic auto mechanism at a certain interval of time.

Documents:

621-kol-2004-granted-abstract.pdf

621-kol-2004-granted-claims.pdf

621-kol-2004-granted-correspondence.pdf

621-kol-2004-granted-description (complete).pdf

621-kol-2004-granted-drawings.pdf

621-kol-2004-granted-examination report.pdf

621-kol-2004-granted-form 1.pdf

621-kol-2004-granted-form 13.pdf

621-kol-2004-granted-form 18.pdf

621-kol-2004-granted-form 2.pdf

621-kol-2004-granted-form 3.pdf

621-kol-2004-granted-form 5.pdf

621-kol-2004-granted-gpa.pdf

621-kol-2004-granted-reply to examination report.pdf

621-kol-2004-granted-specification.pdf

621-kol-2004-granted-translated copy of priority document.pdf