Agglomerating cyclone of the reverse-flow type

Abstract

A family of optimised cyclones has been surprisingly detected, when incorporating into cyclone calculation the interparticle agglomeration phenomenon, the main cause of the capture of submicrometric particles by greater particles preferably having diameters of 10-20 m, the family of optimised cyclones having a geometry defined by the following non-dimensional parameters: a/D 0.110-0.170; b/D 0.110-0.170; s/D 0.500-0.540; D e/D 0.100-0.170; h/D 2.200-2.700; H/D 3.900-4.300; D b/D 0.140-0.180, wherein a and b are the sides of the tangential cyclone entrance, which has a rectangular cross-section, and the first of these sides is parallel to the axis of the cyclone, which has a body of height H with a cylindrical upper section having an inner diameter D and a height h, and a lower section with an inverted truncated cone shape with a minor base having the diameter D b; and a cylindrical vortex tube of height s and diameter De (inner dimensions). Global efficiency is maximised in that the efficiency for finer and/or less dense particles, which are the most difficult to capture, is maximised.

Claims

1. Agglomerating cyclone of the reverse-flow typecomprising a tangential entry of rectangular cross section, of sides a and b, the first parallel to the main cyclone axis; a body of total height H with an upper cylindrical part of internal diameter D and height h and with a bottom inverted conical part whose smaller base has the smaller diameter D.sub.b; and one cylindrical vortex tube of height a and diameter D.sub.epresenting a geometry, defined in terms of ratios of the internal dimensions of the referred sides, heights and diameters to the internal diameter D of the cyclone body, according to the following net of intervals of values, relative to the following non-dimensional ratios: TABLE-US-00006 a/D 0.110-0.170; b/D 0.110-0.170; s/D 0.500-0.540; D.sub.e/D 0.100-0.170; h/D 2.200-2.700; H/D 3.900-4.300; D.sub.b/D 0.140-0.180.

2. Cyclone according to claim 1, wherein the dimension of the sides a and b are equal, such that the entry section is squared.

3. Cyclone according to claim 1, wherein the entry section is of a volute type.

4. De-dusting method of a gaseous stream, wherein the gaseous stream circulates through a device according to claim 1.

5. De-dusting method according to claim 4, wherein a gaseous stream carrying particles with true density below 1000 kg/m.sup.3 circulates through a device according to claim 1.

6. De-dusting method according to claim 4, wherein a gaseous stream carrying particles with a cumulative fraction (mass or volume) below 10-20 m in the range of 90% to 100% circulates through a device according to claim 1.

7. De-dusting method according to claim 4, wherein a gaseous stream carrying particles with a sub-micrometric cumulative fraction (mass or volume) in the range of 20% to 30% circulates through a device according to claim 1.

8. De-dusting and acid gas dry cleaning method, from a gaseous stream, according to claim 4, wherein, upstream to the cyclone, an appropriate reactant in powder form is injected for acid gas removal.

9. Use wherein the device of claim 1 and corresponding method of claim 8 are employed for de-dusting and cleaning of acid gases.

10. Use according to claim 9, wherein the acid gases are HCl (hydrogen chloride), HF (hydrogen fluoride), SO.sub.2 (sulphur dioxide) and/or NOx (nitrogen oxides).

11. Use wherein the device of claim 1 and the corresponding method of claim 4 are employed for de-dusting of flue gases from diesel engines.

Description

5BRIEF DESCRIPTION OF FIGURES

(1) FIG. 1 represents a reverse-flow cyclone and shows the linear dimensions that are the basis for calculating the non-dimensional ratios referred before, dimensions which were already described in detail, as well as the flows entering and exiting the cyclone, respectively the dirty gas (GS) the cleaned gas (GL) and the captured particles (P).

(2) FIG. 2 represents a typical agglomerating cyclone according to the invention (HR_MK).

(3) FIG. 3 represents a graph with the particle size distribution used in a small cyclone according to the invention (HR_MK) of 135 mm internal diameter (D) for a very low particle density (.sub.p) of 450 kg/m.sup.3. The ordinate axis represents the cumulative undersize frequency (FC) in percentage (by Volume) and the abscissa axis the diameter () of the particles, in microns.

(4) FIG. 4 represents a graph where the grade-efficiencies are compared for the geometry of the invention (HR_MK) and for the geometry Cyclop_HE (for the particles of FIG. 3). The ordinate axis represents the efficiency () and the abscissa axis the diameter () of the particles, in microns.

(5) FIG. 5 represents a graph with the particle size distribution used in a cyclone according to the invention (HR_MK) of 460 mm internal diameter (D) for a particle density (.sub.p) of 906 kg/m.sup.3. The axes are identical to those of FIG. 3.

(6) FIG. 6 represents a graph where the grade-efficiencies are compared for the geometry of the invention (HR_MK) and for the geometry Cyclop_HE (for the particles of FIG. 5). The axes are identical to those of FIG. 4.

(7) FIG. 7 represents a graph with the particle size distribution used in a cyclone according to the invention (HR_MK) of 700 mm internal diameter (D) for a very low particle density (.sub.p) of 310 kg/m.sup.3. The axes are identical to those of FIG. 3.

(8) FIG. 8 represents a graph where the grade-efficiencies are compared for the geometry of the invention (HR_MK) and for the geometry Cyclop_HE (for the particles of FIG. 7). The axes are identical to those of FIG. 4.

(9) FIG. 9 represents a graph with the particle size distribution used in a cyclone according to the invention (HR_MK) of 1400 mm internal diameter (D) for a large particle density (.sub.p) of 1450 kg/m.sup.3. The axes are identical to those of FIG. 3.

(10) FIG. 10 represents a graph where the grade-efficiencies are compared for the geometry of the invention (HR_MK) and for the geometry Cyclop_HE (for the particles of FIG. 9). The axes are identical to those of FIG. 4.

6SPECIFIC EXAMPLES

(11) To confirm the simulation results obtained, four different sized cyclones were tested according to the invention (HR_MK), with diameters of 135, 460, 700 and 1400 mm. The obtained efficiencies with different particles and particle size distributions were compared with those obtained with similar sized cyclones of the type Cyclop_HE (the best numerically optimized prior to the present invention), for the capture of very fine powders, with very low density or with both of these characteristics. In all cases, a significant increase in the capture efficiencies of fine particles was observed, and consequently, of the global efficiency.

(12) The comparison between the geometries HR_MK and Cyclop_HE was also done for a case of denser particles and without any appreciable size fraction below 1 micron, end even below 10 micron, where, in this case, the geometry Cyclop_HE was better.

(13) 6aHR_MK of 135 mm

(14) FIG. 3 shows the test particle size distribution for a cyclone of the present invention (HR_MK) of 135 mm diameter, for non-porous particles but of very low density (true density, obtained by helium pycnometry, of 450 kg/m.sup.3). The remaining operating conditions were: gas flow-rate of 40 m.sup.3/h@165 C. and inlet concentration of 530 mg/m.sup.3. FIG. 4 compares the performance of the cyclones HR_MK and Cyclop_HE (EP0972572), for an equivalent pressure drop (2.6 kPa). It should be noted that low particle density enhances inter-particle agglomeration by producing cohesive particle collisions (Paiva et al., 2010). Global efficiencies were respectively of 57 and 76% for the geometry Cyclop_HE and for the optimized HR_MK, i.e., emissions of the optimized cyclone according to the present invention are about 56% lower than those of the Cyclop_HE.

(15) 6bHR_MK of 460 mm

(16) FIG. 5 shows the test particle size distribution for a cyclone of the present invention (HR_MK) of 460 mm de diameter, for particles with a skeletal density (including the intra-particle pores) obtained by mercury pycnometry, of 906 kg/m.sup.3) (for non-porous particles the true density coincides with the skeletal density, but for porous particles the skeletal density is always lower than the true density and is the one that should be used in cyclone modelling). The remaining operating conditions were: gas flow-rate of 310 m.sup.3/h@30 C. and inlet concentration of 430 mg/m.sup.3. FIG. 6 compares the performance of the cyclones HR_MK and Cyclop_HE (EP0972572), for an equivalent pressure drop (1.8 kPa). Global efficiencies were respectively of 62 and 92% for the geometry Cyclop_HE and for the optimized HR_MK, i.e., emissions of the optimized cyclone according to the present invention are about 78% lower than those of the Cyclop_HE.

(17) 6cHR_MK of 700 mm

(18) FIG. 7 shows the test particle size distribution for a cyclone of the present invention (HR_MK) of 700 mm de diameter, for particles with a skeletal density of 310 kg/m.sup.3. The remaining operating conditions were: gas flow-rate of 640 m.sup.3/h@20 C. and inlet concentration of 360 mg/m.sup.3. FIG. 8 compares the performance of the cyclones HR_MK and Cyclop_HE, for an equivalent pressure drop (1.9 kPa). The emissions of the optimized cyclone according to the present invention are about 75% lower than those of the Cyclop_HE.

(19) 6dHR_MK of 1400 mm

(20) In this case (FIGS. 9 and 10), the particles used were denser and without an appreciable sub-micrometer fraction, with only 20% below 10 m, thus with a lower tendency for agglomeration as compared to less dense and finer particles. The geometry according to the present invention (HR_MK) is not superior to the geometry Cyclop_HE, for equivalent pressure drops (1.2 kPa), for particles with density 1450 kg/m.sup.3, gas flow-rate of 72000 m.sup.3/h@88 C. and an inlet concentration of 460 mg/m.sup.3.

7FINAL COMMENTS

(21) The geometry HR_MK is the one that maximizes efficiency, considering inter-particle agglomeration and minimizing particle re-entrainment. The geometry HR_MK was tested at pilot and industrial-scales, showing significantly higher efficiencies (emissions, on average, 70% lower) than those from a very high efficiency cyclone available in the literature and in the marketplace and patented (EP0972572).

(22) The geometry HR_MK is significantly different from high efficiency geometries available in the marketplace, being the only one, to the knowledge of the inventorsl, which was numerically optimized taking inter-particle agglomeration into account.

(23) Predicted behaviour for industrial-scale situations show that the proposed geometry will have significantly higher efficiencies than those of the most efficient cyclones available in the marketplace, as long as particles to be captured have low densities and with a significant sub-micrometer fraction and also below about 10-20 m, with expected emission reductions, on average of 70% relative to the Cyclop_HE geometry.

(24) The method and the cyclone according to the invention are particularly preferential for the capture of particles with true densities below 1000 kg/m.sup.3, when transported in a gas.

(25) The method and the cyclone according to the invention are particularly preferential for the capture of particles from flue gases where the sub-micrometric fraction ranges from 20% to 30%.

(26) The method and the cyclone according to the invention are particularly preferential for the capture from flue gases where particles below 10-20 m range from 90% to 100%.

(27) The method and the cyclone according to the invention are even more preferential for the de-dusting of flue gases where particles have any two of the three characteristics given in the three precedent paragraphs, being most preferential for de-dusting of flue gases where the particles combine the three given characteristics.

(28) Considering that the inter-particle agglomeration/clustering promoted by the cyclone according to the invention and respective method is temporary, namely in the cases of the four paragraphs above (specially in the cases of examples 6a to 6c in the preceding section) occurring in the interior of the cyclone and ending when the particles are deposited at its outlet (namely when the particles are collected in any hopper)being such agglomeration a temporary clusteringit was found that such cyclone and method are particularly indicated for the recovery of powdery material carried in gaseous streams. According to a particular embodiment of the invention, after the method of particle capture according to the invention, thus comprising the agglomerates (clusters) of particles formed inside the cyclone, these, after their removal from the cyclone bottom, are subjected to an additional stage of de-agglomeration (clusters' destruction), that complements the natural separation. According to a particular embodiment, the additional de-agglomeration stage can be done dispersing the clusters in a liquid medium.

(29) The geometry of the cyclones according to the invention is substantially different from those existing in the marketplace, as well as from those referred to in the specialized literature, as it only shares, in the worst case, two of the seven ratios that define the cyclone geometry.

(30) The cross section of the entry is preferably of a square configuration, the dimensions a and b being equal.

(31) Although the entry should be of a tangential type, it may be volute, if the size justifies, without invalidating any of the above considerations.

8BIBLIOGRAFIA

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