Title of Invention

APPARATUS FOR CLEANING AND/OR DEDUSTING WASTE GAS STREAMS CONTAINING DUST

Abstract

Apparatus for cleaning and/or dedusting rate-fluctuating streams of waste gas containing dust from steelmaking metallurgical plants, comprising: • a saturator stage, in which the waste gas can be saturated to a relative moisture content of approximately 100%, • a first droplet-separating stage, adjoining the saturator stage, it being possible for over 90% of grit and large, grit-laden droplets from the saturator stage to be separated in the saturator and droplet-separating stages, • a Venturi scrubber, adjoining the droplet-separating stage, comprising: • a converging waste-gas inlet part, • a central part with a rectangular adjustable Venturi throat and means for spraying in water in the region of the Venturi throat, it being possible by using the first means for spraying in water for water to be sprayed into the waste gas essentially transversely with respect to the average direction of waste-gas flow, and • a diverging waste-gas outlet part, • and a second droplet-separating stage, adjoining the Venturi scrubber, in which droplets can be largely removed from the stream of waste gas, characterized in that an additional amount of water is sprayed into the waste-gas duct upstream of the Venturi throat, but downstream of the first droplet-separating stage, by a second means : for spraying in water, to be precise at a rate of 0.2 - 2.0 dm3 of water per 1000 Nm3 of moist waste gas in the form of droplets with a Sauter diameter of < 1000 &#956;n, the second means for spraying in water being arranged at a distance of 1.5*a to 20*a from the Venturi throat, "a" being the width of the Venturi throat at maximum opening.

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10] "APPARATUS FOR CLEANING AND/OR DEDUSTING WASTE GAS STREAMS CONTAINING DUST" VOEST-ALPINE INDUSTRIEANLAGENBAU GMBH, of Turmstrasse 44, A-4020 Linz, Austria, The following specification particularly describes the nature of the invention and the manner in which it is to be performed:- The invention concerns an apparatus for cleaning and/or dedusting rate-fluctuating streams of waste gas containing dust from steelmaking metallurgical plants, comprising: • a saturator stage, in which the waste gas can be saturated to a relative moisture content of approximately 100%, • a first droplet-separating stage, adjoining the saturator stage, it being possible for over 90% of grit and large, grit-laden droplets from the saturator stage to be separated in the saturator and droplet-separating stages, • a Venturi scrubber, adjoining the droplet-separating stage, comprising: • a converging waste-gas inlet part, • a central part with a rectangular adjustable Venturi throat and means for spraying in water in the region of the Venturi throat, it being possible by using the means for spraying in water for water to be sprayed into the waste gas essentially transversely with respect to the average direction of waste-gas flow, and • a diverging waste-gas outlet part, • and a second droplet-separating stage, adjoining the Venturi scrubber, in which droplets can be largely removed from the stream of waste gas. On account of the process control used for metallurgical plants, their waste gases often contain combustible gas constituents (essentially carbon monoxide) and/or combustible dust constituents (metallic, for example iron, but also carbon). For safety reasons, wet scrubbers are therefore suitable in particular for the dedusting and cleaning of such waste gases. In comparison with other wet scrubbers, Venturi scrubbers have low investment and maintenance costs, high operational reliability and a high degree of separation in the fine-dust range. Waste gases of metallurgical plants are almost always characterized by a high dust content, a significant proportion being in the form of grit (10 urn up to distinctly above 1 mm) on account of to some extent very high waste gas velocities (owing to the thermal currents caused by high temperatures). A considerable proportion of dust is, however, in the form of fine dust (smaller than 10 μm), which is due to the high process temperatures, to be precise caused by material being vaporized and recondensed, with very fine dust in the form of aerosols being produced during cooling. This usually requires at least two-stage dust separation, grit being separated in the first stage to reduce the risk of abrasions and depositions in the subsequent fine-dust separation, and the fine dust being separated in the second stage. The requirements which the fine-dust separation has to meet are becoming increasingly stringent, on account of stricter environmental regulations. There is therefore a need for wet scrubbers with improved efficiency for dust separation. For fine-dust separation, a Venturi scrubber with a fixed throat is the most efficient and also the best in terms of flow control. This only applies, however, to operation at the design point with a constant waste-gas rate. When there is a fluctuating waste-gas rate - which is always the case with steelmaking metallurgical plants - the separating efficiency drops, however, as the waste-gas rate drops, since the pressure loss over the throat likewise drops. Maintaining the pressure loss by increasing the amount of water sprayed in is not cost-effective owing to the higher capacity then required in water preparation (sedimentation). In cases where a fluctuating waste-gas rate must be expected, usually Venturi scrubbers with an adjustable throat are used. In this case, the rectangular throat is adjustable by means of two plates -which are respectively pivotable about an axis at the upper end. The variable throat position makes Venturi scrubbers of this kind significantly more complex in flow terms, in particular also with regard to introducing the scrubbing water. Accordingly, there is provided an apparatus for cleaning and/or dedusting rate-fluctuating stream of waste gas containing dust from steelmaking metallurgical plants, comprising: • a saturator stage, in which the waste gas can be saturated to a relative moisture content of approximately 100%, • a first droplet-separating stage, adjoining the saturator stage, it being possible for over 90% of grit and large, grit-laden " droplets from the saturator stage to be separated in the saturator and droplet-separating stages, • a Venturi scrubber, adjoining the droplet-separating stage, comprising: • a converging waste-gas inlet part, • a central part with a rectangular adjustable Venturi throat and means for spraying in water in the region of the Venturi throat, it being possible by ' using the first means for spraying in water for water to be sprayed into the waste gas essentially transversely with respect to the average direction of waste-gas flow, and • a diverging waste-gas outlet part, • and a second droplet-separating stage, adjoining the Venturi scrubber, in which droplets can be largely removed from the stream of waste gas, characterized in that an additional amount of water is sprayed into the waste-gas duct upstream of the Venturi throat, but downstream of the first droplet-separating stage, by a second means ; for spraying in water, to be precise at a rate of 0.2 - 2.0 dm3 of water per 1000 Nm3 of moist waste gas in the form of droplets with a Sauter diameter of It is therefore the object of the present invention to provide a wet scrubber which ensures efficient separation of fine dusts when there are fluctuating waste-gas rates. This object is achieved according to the invention by an additional amount of water being sprayed into the waste-gas duct upstream of the Venturi throat, but downstream of the first droplet-separating stage, by a further means for spraying in water, to, be precise at a rate of 0.2 - 2.0 dm3 of water per 1000 Nm3 of moist waste gas in the form of droplets with a Sauter diameter of The additional spraying in of water under the conditions specified above creates additional droplet surface areas, which together with their relative velocity with respect to the dust particles produce an increased number of collisions between dust particles and droplets and therefore improve the separating capacity. It is essential here that the further means- for spraying in water is arranged at the distance specified according to the invention of 1.5*a to 20*a from the Venturi throat. Additional spraying in of water outside this range (> 20*a) does not lead to the high separating capacity achieved with the present invention. On account of droplet enlargement on the way to the Venturi throat, the droplets in the throat are no longer available as "fine" droplets. Additional spraying in of water below 1.5*a is likewise not desired, because then the droplet velocities to be achieved when spraying in water would have to be very high already and, what is more, the spraying in of water at high velocity would destroy the flow in the Venturi throat. The term "grit", as it is used here, comprises dust particles with a diameter of > 10 μm. "Large" droplets, as referred to those separated in the first droplet-separating stage, are understood to mean droplets with a diameter of > 1 mm. The Sauter diameter is that diameter of a droplet which has the same volume/surface area ratio as a complete spraying test. It is therefore a measure of the ratio of droplet volume to droplet surface area. A smaller Sauter diameter therefore means a larger surface area. When it is said that droplets are "largely" separated in the second droplet separator, this is understood here to mean over 99% separation. In the region of the Venturi throat, it is essential to achieve the highest possible relative velocity between the water droplets sprayed in there and the dust particles. Therefore, water is sprayed in there essentially transversely with respect to the average direction of waste-gas flow, "transversely" being understood to mean an angle of 30 to approximately 90°. The further means for spraying in water is advantageously arranged at a distance of 2*a to 12*a, preferably of 4*a to 10*a, from the Venturi throat. A particularly high separating capacity is achieved in the range from 2 to 12*a, or in the preferred range of 4 to 10*a. According to a preferred embodiment, the further means for spraying in water is formed by a plurality of nozzles distributed over the cross section of the' waste-gas duct. This makes it possible to subject the entire stream of waste gas to an additional amount of water. According to an advantageous feature, droplets with a Sauter diameter of Since the droplet surface areas, and consequently the droplet diameters, play a significant role in the separation, it is of advantage if the diameters of the droplets sprayed in are as small as possible. A particularly high separating capacity is achieved in the range of a Sauter diameter of up to 400 μm. According to a further advantageous feature, the further means for spraying in water is arranged in such a way that it allows droplets to be sprayed into the waste-gas duct essentially concurrently with the stream of waste gas. "Essentially concurrently" is understood here to mean an angle of 0 to 45° with respect to the average direction of waste-gas flow prevailing at the spraying-in location. A further advantageous embodiment consists in that the further means for spraying in water is designed in such a way that it allows droplets to be sprayed in at a velocity which is at least equal to the average waste-gas flow velocity prevailing at the spraying-in location. On the one hand, this allows the separating effect of the droplets to be utilized twice, on account of the difference in velocity between droplets and dust particles prevailing at the latest in the throat, on the other hand the loss in flow caused by the means for spraying in water is compensated again by the concurrent spraying in at higher velocities. This allows the highest possible relative velocity between sprayed-in droplets and dust particles to be set. The invention is explained in more detail below on the basis of the exemplary embodiment represented in Figure 1. Figure 1 shows the apparatus according to the invention, comprising saturator stage 1, first droplet-separating stage 2, Venturi scrubber 3 and second droplet-separating stage 4. Dust-laden waste gas 5 is introduced into the saturator stage 1. The saturator stage 1 is designed here as a simple Venturi scrubber with a fixed throat. A further possible embodiment of the saturator stage 1 is, for example, a nozzle scrubber. Water 6 is sprayed into the saturator stage and the waste gas is saturated to a relative moisture content of approximately 100%. In the first droplet-separating stage 2, adjoining the saturator stage 1 and designed here as a baffle-plate separator, over 90% of the grit, or the grit-laden droplets, is separated. Separated dust and water are drawn off via a sludge-discharge line 7. The first droplet-separating stage 2 is followed downstream by a Venturi scrubber 3 with a converging waste-gas inlet part 8, adjustable throat 9 and diverging waste-gas outlet part 10, the distance indicated by "a" representing the width of the Venturi throat 9 at maximum opening. Water can be sprayed into the region of the Venturi throat 9, by means for spraying in water 11, into the waste gas transversely to the average direction of waste-gas flow. Arranged in the waste-gas duct downstream of the first droplet-separating stage 2 are nozzles 12, to be precise at a distance of approximately eight times the maximum width of the Venturi throat 9. Water is additionally sprayed into the waste gas through these nozzles 12. Dedusted/clean gas is drawn off via a clean-gas discharge line 13 and separated water from the further droplet-separating stage 4 is drawn off via a recycled-water discharge line 14. This recycled water may be advantageously used for spraying in in the saturator stage 1. Example 1: dust separation from steelworks waste gas Waste-gas rate: fluctuating in the range of 40000 - 80000 Nm3/h Dust content: approximately 100 g/Nm3 The saturator stage is designed in the form of a simple Venturi scrubber (with fixed throat) with a low pressure loss of 15 - 35 mbars - depending on the waste-gas rate - (low-pressure Venturi scrubber). Grit with diameters > 10 μm is predominantly separated. This is required to avoid excessive abrasion in the downstream Venturi scrubber, where high waste-gas velocities in the range from 50 to over 150 m/s occur, to be precise according to the required clean-gas dust content. The droplet separator is designed as a baffle-plate separator. Droplet separation is necessary because the droplets already have a high burden of solids in the form of abrasive particles - up to 20 g/L - before they enter the Venturi scrubber. Venturi scrubber with adjustable rectangular throat: width at maximum opening: 300 mm The L/G ratio in the region of the Venturi throat can be set between 2.7 - 4.7 dm3/1000 Nm3, according to the waste-gas rate. Differential pressure: approximately 140 mbar Arranged in a cross-sectional plane of the Venturi scrubber above the throat are 13 nozzles, this cross-sectional plane being at a distance of 3000 mm from the throat. The additional L/G ratio at the 13 nozzles is - depending on nozzle operation and waste-gas rate - 0.2 - 1.0 dm3/1000 Nm3, with a Sauter diameter of 80 - 200 μm. Table 1 Outlet dust content without additional nozzles 60 - 100 mg/Nm3 L/G ratio at nozzles Additional dust reduction 0.4 - 28% 1.0 - 52% Example 2: test plant Waste-gas rate Dust content: Saturator: Droplet separator Venturi scrubber: can be set between 500 and 1600 Nm3/h can be set between 5 and 20 g/Nm3 simple nozzle scrubber low pressure loss of 1 - 5 mbar, depending on waste-gas rate separation of a large part of the grit (> 10 μm) lamellar separator adjustable rectangular throat (max. opening width: 700 mm) L/G ratio (throat): l-5dm3/Nm3 Differential pressure: 100 - 140 mbar 2-4 nozzles over cross section, 1.5*70 cm in stages up to 40*70 cm away from throat. Additional L/G ratio at nozzles: 0.2-4 dm3/Nm3 Sauter diameter: 50 - 2000 μm) Outlet dust content without nozzles can be set from 30 - 200 mg/Nm3 Table 2: Variation in L/G ratio: L/G ratio Additional dust reduction 0.1 - 5% 0.3 - 15% 1.0 - 62% 3.5 - 35% Variation in Sauter diameter: Sauter diameter Additional dust reduction 2000 ± 0% 500 - 12% 250 - 23% 120 - 40% 60 - 55% Variation in distance: Distance Additional dust reduction 1.5*a - 45% 10*a - 55% 20*a - 40% 40*a - 25% WE CLAIM:- 1. Apparatus for cleaning and/or dedusting rate-fluctuating streams of waste gas containing dust from steelmaking metallurgical plants, comprising: • a saturator stage, in which the waste gas can be saturated to a relative moisture content of approximately 100%, • a first droplet-separating stage, adjoining the saturator stage, it being possible for over 90% of grit and large, grit-laden droplets from the saturator stage to be separated in the saturator and droplet-separating stages, • a Venturi scrubber, adjoining the droplet-separating stage, comprising: • a converging waste-gas inlet part, • a central part with a rectangular adjustable Venturi throat and means for spraying in water in the region of the Venturi throat, it being possible by using the first means for spraying in water for water to be sprayed into the waste gas essentially transversely with respect to the average direction of waste-gas flow, and • a diverging waste-gas outlet part, • and a second droplet-separating stage, adjoining the Venturi scrubber, in which droplets can be largely removed from the stream of waste gas, characterized in that an additional amount of water is sprayed into the waste-gas duct upstream of the Venturi throat, but downstream of the first droplet-separating stage, by a second means : for spraying in water, to be precise at a rate of 0.2 - 2.0 dm3 of water per 1000 Nm3 of moist waste gas in the form of droplets with a Sauter diameter of 2. Apparatus as claimed in claim 1, wherein the second means for spraying in water is arranged at a distance of 2*a to 12*a, preferably of 4*a to 10*a, from the Venturi throat. 3. Apparatus as claimed in claim one of claims 1 or 2, wherein the second means for spraying in water is formed by a plurality of nozzles distributed over the cross section of the waste-gas duct. 4. Apparatus as claimed in claim one of claims 1 to 3, wherein droplets with a Sauter diameter of 5. Apparatus as claimed in one of claims 1 to 4, wherein the second means for spraying in water is arranged in such a way that it allows droplets to be sprayed into the waste-gas duct essentially concurrently with the stream of waste gas. 6. Apparatus as claimed in one of claims 1 to 5, wherein the second means of spraying in water is designed in such a way that it allows droplets to be sprayed in at a velocity which is greater than or at least equal to the average waste-gas flow velocity prevailing at the spraying-in location. 7. Apparatus for cleaning and/or dedusting rate-fluctuating streams substantially as hereinbefore described with reference to the accompanying drawings. Dated this 12th day of May, 2000 [JAYANTA PAL] OF REMRRY & SAGAR ATTORNEY FOR THE APPLICANTS]

Documents:

441-mum-2000-cancelled pages(20-01-2005).pdf

441-mum-2000-claims(granted)-(20-01-2005).doc

441-mum-2000-claims(granted)-(20-01-2005).pdf

441-mum-2000-correspondence(16-05-2007).pdf

441-mum-2000-correspondence(ipo)-(13-02-2007).pdf

441-mum-2000-form 1(12-05-2000).pdf

441-mum-2000-form 19(19-04-2004).pdf

441-mum-2000-form 2(granted)-(20-01-2005).doc

441-mum-2000-form 2(granted)-(20-01-2005).pdf

441-mum-2000-form 3(12-05-2000).pdf

441-mum-2000-form 3(20-01-2005).pdf

441-mum-2000-form 3(31-10-2000).pdf

441-mum-2000-form 5(12-05-2000).pdf

441-mum-2000-petition under rule137(20-01-2005).pdf

441-mum-2000-petition under rule138(20-04-2005).pdf

441-mum-2000-power of authority(04-09-2000).pdf

441-mum-2000-power of authority(05-09-2000).pdf

441-mum-2000-power of authority(20-01-2005).pdf

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