PT972572E - High efficiency cyclones - Google Patents

Abstract

The present invention concerns high efficiency reverse flow cyclones - with a tangential entry of essentially rectangular section, sides a and b, the first parallel to the cyclone axis; a body of height H, with an upper cylindrical section of diameter D and height h and a lower inverted cone with smaller base of diameter Db: and a cylindrical vortex finder of diameter De and length s - which may be used in laboratory or industrial conditions, whenever dedusting is needed. The inventor could obtain an empirical correlation to estimate particle turbulent diffusivities under cyclone flow, through the use of a finite diffusivity theory which was adjusted to laboratory, pilot-scale and industrial grade efficiency curves. This correlation allows the design of reverse-flow cyclones of arbitrary geometry, as a function of particle size distribution and operating conditions. A computer program was made to obtain optimum designed reverse-flow cyclones, and two geometries have been obtained, which respectively maximise collection efficiency and one ratio efficiency/costs. The proposed geometries, defined as ratios of the above mentioned dimensions to the cyclone inside diameter, differ from all geometries available in the literature, both being significantly more efficient. For flow rates typical of industrial multicyclones, the emissions should be 30-45% lower for the first family and 20-35% for the second, as compared with emissions from high efficiency cyclones available. Laboratory-scale tests with a similar geometry have confirmed the expected emissions reductions, at similar levels of pressure drop. <IMAGE>

Description

DESCRIPTION &quot; HIGH EFFICIENCY CYCLONES &quot;

Technical Field The present invention, respecting cyclones, is in the field of dedusting equipment.

Cyclones are indeed disposers used in various types of industries with two complementary purposes: removal of dust from the gases emitted by processes, before being released into the air (eg boiler fumes), and dust recovery useful as a raw material for the processes that generated them (eg wood, cork and metal-mechanical industries).

BACKGROUND ART Industrial cyclones are of various types, the most commonly used are those of the inverted flow type, the scheme of which is shown in figure 1. The gas enters through section ab and is required to describe a downward spiral until which changes direction due to the established pressure field (hence the designation &quot; inverted flow &quot;) coming out at the top by the vortex tube of height if diameter De.In its downward path the particles are dragged to the walls and eventually fall at the bottom of the cyclone, part of which is separated from the gas.

Cyclone manufacturers specify their projects through &quot; families &quot;, characterized by having fixed relationships of certain internal internal dimensions, namely the seven ratios of a, b, s, De, h, H and Db relative to to the inside diameter D.

[0005] Although the first cyclones date back to the nineteenth century, there is certainly no model of calculation that can be reliably applied to the inverted-flow cyclone project. There is only one theory that can reasonably adjust many of the existing data on laboratory and pilot cyclones or industrial scale and was developed by Mothes and Loffler (1988), theory hereinafter referred to as ML theory. Its disadvantage is that it can only be used as a diagnosis (adjustment of results obtained with existing cyclones) and not as a prognosis (or prediction of the behavior of cyclones with arbitrary geometry). The problem lies in not knowing the value of the turbulent diffusivity of the particles, fundamental parameter in ML theory and the way in which it is affected by geometry, operative conditions and granulometry.

Some researchers have looked at this subject, including the Applicant himself (Clift et al., 1991, Salcedo, 1993, 1996, Salcedo and Fonseca, 1996). However, until recently (Salcedo and Coelho, 1999), it was not possible to describe this parameter through any usable relationship in the cyclone project.

Thus, the problem of obtaining more efficient geometries has been addressed through the empirical path (by trial and error), as demonstrated by the few existing works on the subject (Li et al., 1988; Schmidt, 1993) . While these methods lead to improved projects, the improvements are generally not very significant, requiring too much time and cost of development.

In short, reverse-flow cyclones on the market are certainly not the best, ie the most efficient and at the same time low energy consumption. Cyclone manufacturers are designing these equipment based primarily on their experience and empirical knowledge.

In any case, a more detailed comparison between the cyclones according to the present invention and those of the prior art, namely that corresponding to patent EP0564992 and nine others collected essentially from examples in the literature, will be made below, both after the Description of the invention at the end of the respective chapter, as well as in the Practical examples chapter.

A new approach In order to achieve efficiently cyclone projects significantly higher than the cyclones available on the market, a study was first carried out on the applicability (adjustment) of the ML theory to the fractional efficiency curves (efficiency versus dust size) of 21 cases reported in the literature. The cyclones studied range from 0.03658m to 0.305m in diameter D and flow rates from 0.7m3h-1 to 835m3h-1, that is, both laboratory conditions and pilot and industrial scale conditions were studied. The turbulent diffusivities obtained in the 21 adjustments were then correlated with the granulometry, cyclone geometry and operating conditions (flow rate and temperature). After a considerable effort, an empirical correlation explaining 70% of the variability of the data was obtained, which is statistically significant with a high degree of confidence (95%), that is, a correlation that can be reliably used for the project of new cyclones and prediction of their efficiency. Correlation is given by (Salcedo and Coelho, 1999):

Pe = A-ReB (1) where A and B are two constants, Pe is the Peclet number, which depends on the turbulent diffusivity of the particles, and Re is the Reynolds number, which depends on the geometry and operating conditions. The operating conditions, when coupled to the ML theory and the cyclone geometry, give the values of Re. Then, the value of Pe is extracted from the correlation (1), from which the value of the turbulent diffusivity of the particles is extracted directly. This correlation produces much better results than considering a constant value for diffusivity, as proposed by some authors (Clift et al., 1991; Hoffmann et al., 1996) or by another correlation proposed in the literature (Ogawa, 1984, 1987; Li and Wang, 1989).

In a second phase, a computer program was developed that optimizes cyclone geometry based on two different criteria: maximum efficiency or maximum efficiency / cost ratio, in this case the investment and operating costs estimated by the criterion of Licht (1980), which defines an adimensional parameter, KLiChtl which is to be maximized. The computer program uses the ML theory with the diffusivity taken from the correlation (1) and matches it with an optimization routine developed by the proposer (Salcedo, 1992). As constraints to the optimization, several geometric criteria were imposed to allow obtaining cyclones with viability of construction, and criteria of maximum allowed pressure drop, which was fixed at approximately 1500Pa (150mmH2O), as is common in industrial applications of this type of equipment. It was also included, as a restriction, that the geometry obtained did not lead to the phenomenon of resuspension of dust (emission to the atmosphere by entrainment of particles previously captured), using the Kalen and Zenz criterion (Licht, 1980). That is, it was intended that the optimized cyclones would have a design efficiency as close as possible to the actual one.

Since the optimization results obtained in the second phase provided geometries that varied according to the operating conditions, it was necessary to proceed with additional simulations in an attempt to obtain a single geometry for each of the two previously set optimization criteria (maximum efficiency or maximum efficiency / cost ratio). This exercise has led to hundreds of simulations / optimizations until we can identify common features defining two families of cyclones, hereinafter referred to as cyclone (s) A and cyclone (s) B.

Description of the Invention High efficiency inverted flow cyclones according to the invention - which are of the type that comprise either a substantially rectangular cross-section tangential inlet, sides a and b, the first of which is parallel to the axis of the cyclone, or a body of height H with a cylindrical upper section of diameter D and height h and a lower inverted truncated conical section with a smaller base of diameter Db or a cylindrical vortex tube of diameter De and height s - the geometry of which was obtained according to the above family, A or B (the first for maximum efficiency cyclones and the second for cyclones which maximize the KLiCht parameter, ie the efficiency / cost ratio) , in that said sides, heights and diameters are related to one another so that the ratios of the respective internal dimensions by the dimension of said internal diameter D of the cyclone body are computed between the (dimensionless) limit values in the first seven rows of Table 1.

[0014] As shown in the table below, the seven key dimensions of the above-mentioned key dimensions, whose limit values are represented in the first part, contain two additional lines: one relative to the dimensionless parameter relative to the cone height (H / Dh / D) and the other parameter KLicht.

Table 1 - Optimized Family Geometries Ratio Cyclones A Cyclones B a / D 0,270-0,360 0,270-0,310 b / D 0,270-0,360 0,270-0,310 s / D 0,330-0,495 0,330-0,395 De / D 0,280-0,370 0,405-0,430 h / D 1,001-1,300 2,050-2,260 H / D 4,050-4,250 3,500-3,700 Db / D 0,200-0,300 0,250-0,300 (Hh) / D 2,750-3,250 1,240-1,650 KLicht 59,0 124,7 For verification of that the proposed geometries are very different from those available on the market, the values of the same ratios in Table 1 are shown in Table 2, but in relation to the geometries available in the literature.

Table 2 - Family geometries available in the literature Ratio (1) (2) (3) (4) (5) (6) (7) (8) (9) a / D 0, 544, 0, 500, 500 0, 750 0, 500 0, 440 0, 500 0, 583 0, 635 b / D 0, 306, 230 0, 200 0, 375 0, 250 0, 210 0, 250 0, 208 0, 279 s / D 0, 544, 654 0, 500 0, 875 0, 625, 500 0, 600 0, 583 0, 500 De / D 0, 500 0, 523 0, 500 0, 750, 0, 0, 400 , 500 0, 500 0, 583 h / D 0, 544 0, 654 1, 500 1, 500 2, 000 1, 400 1, 750 1, 333 1, 750 H / D 2, 988 3, 165 4, 000 4,000, 3,000, 3,950, 3,170,300, 7,500 Db / D 0, 500, 0,317, 0,35 0, 3,300 0, 250, 0, 400, 0, 400, 0, 400, 400 Hh) / D 2, 444 2, 511 2, 500 2, 500 2, 2000, 2, 500, 2, 1, 837 2, 100, Licht 9, r 04 24, 33 46, 94 1, 73 25.45 41.21 25.10 27.57: 10.25 [0016] The nine cyclones to be used are: Table 2 is shown in Table 3.

Table 3 - Cyclone Discrimination in Table 2

Cyclone 1 Almeida (1980). Cyclone for boiler fumes 2 Li et al. (1988). Cyclone Zhou # 8 3 Licht (1980). Cyclone Stairmand HE 4 Licht (1980). Cyclone Stairmand HT 5 Licht (1980). Cyclone Lapple 6 Licht (1980). Cyclone Swift HE 7 Licht (1980). Cyclone Swift GP 8 Licht (1980). From the comparison of the values in Tables 1 and 2, it can be seen that Cyclones A have all ratios of key dimensions different from all other nine cyclones except in three cases, where, however, the differences are enormous because only one ratio is punctually common and the remaining six are all different. In the case of Cyclones B, the situation in number is precisely the same.

[0018] The main features that distinguish the optimized families from the rest include, among others that can be extracted from the tables, the following: - Entry of the gas through a preferably square and non-rectangular section; - Vortex tube narrower (De / D minor) and higher cone (H / D-h / D major), in cyclones A; - Higher cylindrical body (h / D higher) and lower cone (H / D-h / D minor), in cyclones B; - High Kncht value.

Also, in order to verify that the proposed geometries are very different from those corresponding to the cyclones described in EP0564992 - for cyclones 10 - the values of the same ratios in table 1 are shown in table 4, but for these cyclones:

Table 4 - Cyclone geometry EP0564992 Ratio (10) a / D 0,274-0,500 b / D 0,141-0,258 s / D 0,270-0,750 De / D 0,300-0,700 h / D 0,160-1,000 H / D 0,800-2,000 Db / D &lt; 2.511 K-Lichl 80 From the comparison of the values in Tables 1 and 4, it is found that both cyclones A and B have four of the seven key dimensions ratios integrally different from those of cyclones 10, cyclones A further having two of the remaining key dimensions ratios partially distinct from those of cyclones 10 and cyclones B, one of which is also partially distinct.

As the main features which distinguish optimized families from cyclones 10, among others which can be extracted from tables 1 and 4, the following stand out: - Entry of the gas through a preferably square and non-rectangular section; - Higher cone (H / D-h / D higher), in all cyclones A, and narrower vortex tube {From / D minor) for part of them; - Higher cylindrical body [h / D higher] and higher Knctit factor, in cyclones B.

On the other hand, Cyclones B in relation to Cyclones A are characterized by the technical characteristics of the first three and the last of the key dimensions ratios having strong common features resulting from the respective limit values defined for each of these ratios of cyclones B, subsets within the intervals of the corresponding ratios of cyclones A. More precisely, in the case of the first two ratios, a union trace between the entrances cyclones of the two types.

Accordingly, the present application relates to two families of inverted-flow cyclone geometries, which have been optimized by computer, having geometric characteristics substantially different from those of the cyclones on the market and both being significantly more efficient . The family of cyclones A is of maximum efficiency and the family of cyclones B, being of slightly smaller efficiency, has, nevertheless, smaller drops of pressure and the respective operative costs are also inferior.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of an inverted-flow cyclone, with indication of its key dimensions; Figure 2 is a proportional representation of the first eight cyclones indicated in table 2, for a diameter D (arbitrary) of 0.02m. The entrances to the first and fourth cyclones are involuntary. Figure 3 is a graph of fractional efficiencies of type A cyclones versus type 3 cyclones (table 2) for various dust diameters. The operating conditions were as follows: flow rate 0.9m3 / h and mean mass diameter of, 37pm. Figure 4 depicts a graph of overall efficiencies of type A cyclones versus various cyclones as represented in Figure 2 (namely, 2, 3, 6 and 8) for various mass flow rates of dust per volume of gas. The operating conditions were as follows: mean mass diameter of 3.67μπι. Figure 5 is a graph similar to that of Figure 4, with respect to the same operating conditions, but with reference to type B cyclones instead of type A. Figure 6 represents, for the same arbitrary diameter of Figure 2, and also proportionally , an example of Cyclone A and Cyclone B.

In order to experimentally confirm the results obtained, 6 mini-cyclones were built, with diameters between 0.0215m and Q0.0m, three of which were Stairmand HE (Licht, 1980) - cyclone number 3 in Table 2 and Figure 2 - and the other three optimized. In all cases a significant improvement in capture efficiency was observed in the optimized ones.

Figure 3 shows the behavior of two mini-cyclones, one cyclone A and the other type 3 being optimized as above. This figure shows the experimental efficiencies (represented by circumferences for cyclone A and circles for cyclone 3) and also, for both cyclones, the efficiencies predicted by ML theory when coupled to the estimation of diffusivity by correlation (1). These efficiencies are represented by a discontinuous line for Cyclone A and a continuous line for Cyclone 3. The dust to be captured is extraordinarily fine as it has a mean diameter (by mass) of 1.37pm. It is the mass distribution that matters to consider since the legislation in force for the emission of particulate matter refers to the mass of dust per volume of gas. The overall efficiencies (resulting from the weighting of the mass fractional efficiencies) were respectively 38% and 55% for Stairmand HE cyclones and optimized, ie the emissions of the optimized cyclone are about 27% lower than those of Stairmand HE cyclone.

The predictions of the behavior of cyclones for industrial situations can be seen in figures 4 and 5, which compare, for very fine dust (3.67pm average mass diameter), the efficiencies estimated for the two optimized families (A and B) and to four known high efficiency families (Licht, 1980; Li et al., 1988). It is notorious the expected efficiency increase of the optimized families. For flows between 100-200m3h-1, typical of industrial multi-cyclones (parallel cyclone batteries), emissions with cyclones A are expected to be 30-45% lower than the high-efficiency cyclones Swift HE and Stairmand HE, respectively (Figure 4). For the geometry of cyclones B, emissions are expected to be about 20-35% lower (figure 5).

In terms of comparison with the cyclones 10 for the same type of dust referred to in figure 4 and, for example, for a flow rate of 110m3h -1, while the efficiency of a cyclone A is 92.5% as extracted from said figure - that of a cyclone 10 having dimensions corresponding substantially to the average value of the preferred ranges of ratios indicated in EP0564992, drops by 78.2% or even by only 65% if one considers the maximum speed allowed to avoid the phenomenon of resuspension. In fact, cyclone 10 can not be considered to be of high efficiency.

Thus, it is estimated that any of the optimized geometries can significantly reduce emissions compared to other high efficiency geometries. These predictions are in agreement with the values obtained in laboratory and presented above.

However, the development of cyclones with efficiencies significantly higher than those of existing cyclones, especially for particles of diameter below 2-3 ppm, has a high potential for industrial application. Many industries (wood, metal-mechanics, cement, chemical production of granulates and powder) could enjoy equipment of low cost and with sufficient efficiency to meet the need to use much more expensive equipment, like filters of sleeves and electrofilters. Even if legislation can only be enforced by means of bag filters or electrofilters, the existence of cyclones of very high efficiency upstream would be largely justified by the protection that cyclones would bring to the more expensive equipment, through less abrasion, erosion and wear. Moreover, in some cases of processes at high temperatures and pressure, cyclones are currently the only despoilers that can be applied.

Bibliographical references [0031] - Almeida, M.J., 'Manual of dust collection in the workplace', Bertrand Bookshop, 1980. - Clift, R., M. Ghadiri and A.C. Hoffman, Ά Critique of Two

Models for Cyclone Performance ', AIChE J., vol.37, 285-289, 1991. - Hoffmann, AC, M. de Groot and A. Hospers,' The effect of the dust collection system on the flowpattern and separation efficiency of a gas cyclone ', Can. J. Chem. Eng., Vol.74, 464-470, 1996. - Li, E. and Wang, Y., "New Theory of Cyclone Separators," AIChE. J., vol.35, no.4, 666-669, 1989. - Li, Z., Z. Zisheng and Yu Kuotsung, "Study of structure parameters of cyclones /, Chem. Eng. Res. Des., Vol. 66, March, 114-120, 1988. - Licht, W., 'Air Pollution Control Engineering-basic cal-culations for particulate collection', Mareei Dekker, New York and Basel, 1980. - Mothes, H. and F. Loffler, 'Prediction of particle removal in cyclone separators' , International Chemical Engineer-ing, Vol. 28, 231-240, 1988. Ogawa, A., "Diffusion of the Fine Solid Particles in the Turbulent Rotational Air Flow in the Vortex Chamber", Bul-Letin of the JSME 27 (226), 763-772 (1984) ). - Ogawa, A., &quot; Diffusion of the Fine Solid Particles on the Concave Wall Surface in the Vortex Chamber &quot;, J. Coll. Engng. Nihon Univ., A-28, 99-109 (1987). - Salcedo, R.L., 'Solving Non-Convex NLP and MINLP Prob-lems with Adaptive Random-Search', Ind. Eng. Chem. Res., Vol. 31, no.1, 262-273, 1992. - Salcedo, R.L., 'Collection Efficiencies and Particle Size Distributions from Sampling Cyclones - Comparison of Recent Theories with Experimental Data', Can. J. Chem. - Salcedo, RL, 'Cyclone simulation - recent advances and comparison with experimental results', 5th National Conference on the Quality of the Environment, vol.l, 783-795, 1996. Eng., Vol.71, 20-27, - Salcedo, RL and AM Fonseca, 'Grade-efficiencies and particle size distributions from sampling cyclones', Mixed-Flow Hydrodynamics, Chapter 23, 539-561, P. Cheremis- inoff (ed.), Gulf Publishers, 1996. - Salcedo, RL and Rabbit 'Turbulent dispersion coeffi cients in cyclone flow: na empirical approach', The Cana-dian Journal of Chemical Engineering, in press 1999. - Schmidt, P., 'Unconventional cyclone separators', Int. Chem. Eng., Vol. 33 (1), 8-17, 1993.

Porto, March 6, 2007

Claims (5)

A high efficiency inverted flow cyclone -integrating a tangential inlet of essentially rectangular cross-section, sides a and b, the first of which is parallel to the axis of the cyclone; a body with a cylindrical upper section of diameter D and height h and with an inverted frustoconical lower portion of base smaller in diameter Db; and a cylindrical vortex tube of height - characterized by having a geometry defined in terms of the ratios of the internal dimensions of said sides, height and diameters by the size of said internal diameter D of the cyclone body, by the set of the following parameters (dimensionless ): a / D b / D s / D Db / D 0.270-0.360; 0,270-0,360; 0,330-0,495; 0.200-0.300. A high efficiency inverted flow cyclone according to the preceding claim, with the body of height H, the respective upper cylindrical section h of height h, and with the cylindrical vortex tube of diameter De - characterized by having a defined geometry , additionally in terms of the ratios of the internal dimensions of said heights and diameter by the size of said internal diameter D of the cyclone body, by the set of the following (dimensionless) parameters: From / D h / DH / D 0.280-0.370; 1,001-1,300; 4,050-4,250. High efficiency inverted flow cyclone according to the first claim - with the height H body, the respective cylindrical upper section h, and the cylindrical vortex tube of diameter De - characterized by having a defined geometry in addition, in terms of the ratios of the internal dimensions of said heights and diameter by the size of said internal diameter D of the cyclone body, by the set of the following (dimensionless) parameters: From / D 0,405-0,430; hr 2.050-2.260; H / D 3,500-3,700; and, in terms of the ratios contained in said first vindication, by its following subsets: a / D 0.270-0.310; b / D 0.270-0.310; s / D 0.330-0.395; Db / D 0.250-0.300. Cyclone according to any of the preceding claims, characterized in that the dimension of the sides a and b is the same, the inlet section being square. Cyclone according to claim 3, characterized by an involute tangential entry. Porto, March 6, 2007