AU712201B2 - Downflow cyclone - Google Patents

Description

I-'IUU/U1 1 2a'519t Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT 4 4 4 9e V 0 4.4 4t 4*

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6V V p 4 *44*VV Application Number: Lodged: Invention Title: DOWANFL(YN CYCLONE The following statement is a full description of this invention, including the best method of performing it known to us A 7772 Metallgesellschaft

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Reuterweg 14 60323 Frankfurt am Main Case No. 93 00 47 Downflow Cyclone Description This invention relates to a downflow cyclone comprising a i: coaxially arranged head portion, a cylindrical separating S chamber and a conical settling chamber as well as raw gas inlet and a gas outlet tube. In this cyclone, the gas stream and the stream of solids leave the separating chamber in parallel in downward direction, i.e. in a falling manner.

The cyclones operate in accordance with the principle of equilibrium, where dust-laden gas (raw gas) flows with a spin into an approximately cylindrical separating chamber, leaves the same again in radially inward direction through the separation surface, an imaginary extension of the gas outlet tube, and then flows axially through the gas outlet tube to the outside. In the process, the dust particles are acted upon by a centrifugal force, which throws the larger particles radially to the outside against the wall. The term gas is used here for any gas as well as mists and vapors. The term dust is meant to include all kinds of particulate impurities which must be removed from the raw gas.

The flow through the cyclone involves a loss of pressure, which is caused by the dissipation of energy when the gas flows into the gas outlet tube, which acts as a throttle.

Moreover, in addition to the main flows there are also produced secondary flows, which above all deteriorate the separation results. This leads to a short-circuit flow along 2 the gas outlet tube, caused by the cooperation of the pinch flow behind the usually present tangential gas inlet and the friction at the lid of the cyclone.

For reducing this short-circuit flow it was suggested to lead the gas inlet away from the lid, or to design the cyclone as a dual cyclone. What is disadvantageous in these types of construction is the fact that moving the gas inlet away leads to an increase in the loss of pressure, and the design as a dual cyclone involves an additional structural effort. A further structural measure described is the design as a continuous-flow cyclone comprising an inner discharge gap and a shielding plate, or comprising a slit immersion tube, an external discharge gap and a boundary layer counter-coil at the bottom. These structural measures are meant to prevent a direct penetration of dust at the separating surface of the lid into the clean gas (Paul .ee Schmidt, "Ungew6hnliche Zyklonabscheider", Chemie-Ingenieur-Technik, 62 (1990), pp. 536 to 543). The above-described types of cyclone separators have the disadvantage of a high number of components required and an increased susceptibility to wear, and they can no longer be safely used at high operating temperatures.

For improving the separation of fine dust particles it was suggested in DE-PS 889 544 to provide conical inserts in a cyclone having a housing conically expanding in the flow direction of the dust-laden air. The raw gas stream entering through a tangential tube leaves the separation chamber in the same direction through a bent gas outlet tube.

The DE-PS 598 423 describes a cyclone having a tangential gas inlet, which includes a downwardly directed gas outlet tube axially protruding into the separation chamber. At its end, the gas outlet tube is provided with an attachment -3which is similar to a flange or forms an angle smaller than 900 with the wall of the tube.

A centrifugal separator group comprising a plurality of cyclones arranged at the same level, which are connected in parallel and include an axial flow, is described in AT-PS 187 516. The raw gas chamber, the clean gas chamber and the dust chamber each extend over the entire group of centrifugal separators. The dust-discharging lines are located in the middle of the axis, and the gas outlet tube is bent.

Finally, the DE-PS 3 225 509 discloses a centrifugal separ- S ator directly connected with a fluidized-bed reactor, which S centrifugal separator has a tangential gas inlet and a gas outlet tube extending from the turbulence chamber. The gas outlet tube extends through the bottom of the turbulence chamber from below, and via an opening disposed at the lowest point of the bottom and a line connected thereto the solid matter is returned to the reactor.

The above-described cyclones all have the disadvantage that secondary flows may form at the point where the raw gas enters the separating chamber, so that dust is moved radi- S ally through the separating surface to the inside and reaches the clean gas stream. In this way, the degree of separation, i.e. the amount of dust separated from the raw gas stream, is reduced.

It is the object of the present invention to improve the degree of separation of a downflow cyclone. In addition, it is the object of the present invention to provide a downflow cyclone which can be used at comparatively high operating temperatures, and where the structural effort and thus the manufacturing costs are kept low.

-I I SUMMARY OF INVENTION According to the present invention, there is provided a downflow cyclone for cleaning dust-laden gases and gaseous substances, said cyclone including a closed head portion, a cylindrical separating chamber arranged coaxially in relation to said head portion and located below said head portion, said cylindrical separating chamber having a height and a diameter, a conical settling chamber arranged coaxially in relation to said separating chamber and located below said separating chamber, 10 a line for discharging solids from said settling chamber, said line being located below said settling chamber, a raw gas inlet passage provided with an inlet opening to the cylindrical separating chamber, said inlet opening having an inlet cross-section at said S separating chamber, said inlet opening being positioned in the lower half of the cylindrical separating chamber, and a gas outlet tube protruding into an interior of the cyclone and having a diameter and an entrance opening into which gas from the separating chamber enters the gas outlet tube; wherein said entrance opening is in an uppermost portion of said gas 20 outlet tube located within said cyclone, said entrance opening is located between an upper theoretical horizontal plane and a lower theoretical horizontal plane, said upper theoretical horizontal plane is a first distance below the head portion, said first distance being equal to the diameter of the gas outlet tube, and said lower theoretical horizontal plane is a second distance below a lowest point of said inlet cross-section, said second distance being up to twice the diameter of the gas outlet tube, a ratio of the height to the diameter of the cylindrical separating chamber is between 1.1:1 and 1.5:1, said gas outlet tube emerges laterally from the conical settling chamber or extends concentrically through said line for discharging solids, and said closed head portion consists of a flat plate.

Preferably, the second distance of the lower theoretical horizontal plane is equal to twice the diameter of the gas outlet tube.

Alternatively, the second distance of the lower theoretical horizontal plane may be equal to the diameter of the gas outlet tube.

In accordance with a preferred embodiment of the invention it is provided that the cross-section of the raw gas inlet be rectangular with a height/width ratio in the range between 1:1 and 5:1.

In accordance with a further preferred embodiment of the invention it is provided that the conical settling chamber have a two-part design, comprising an upper, longer part with an angle of inclination of 20 to 100 and a lower, shorter part with an angle of inclination of 100 to 450.

In accordance with a further preferred embodiment of the invention it is provided that in the conical settling chamber a shielding cone be provided. Due to the installation of a shielding cone, gas bubbles from the line for supplying solids are prevented from penetrating into the separation chamber of the cyclone. Moreover, such a cone has the advantage that it can additionally support the gas outlet tube at the wall of the cyclone.

In accordance with a further preferred embodiment of the invention it is provided that the flow of raw gas into the cylindrical separating chamber be effected through a spiral inlet, a slotted inlet, a tubular inlet, an axial inlet or a helical inlet.

20 In accordance with a further preferred embodiment of the invention it is provided that the point where the gas enters the gas outlet tube be arranged in the conical settling chamber. Especially in the case of a cyclone having a relatively small height/diameter ratio of the cylindrical separating chamber this leads to a comparatively small loss of pressure of the gas in the cyclone with a 25 relatively high degree of separation of solids at the same time.

In accordance with a further preferred embodiment of the invention it is provided that the cyclone be used for cleaning dust-laden gases and gaseous •0 "substances.

In accordance with a further preferred embodiment of the invention it is provided that the cyclone be used as a recirculating cyclone in plants 00comprising a circulating fluidized bed.

o0 comprising a circulating fluidized bed.

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1 1~ 6 In order that the invention might be more fully understood, embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 shows a cross-section through an embodiment of a cyclone as well as a top view and a cross-section of the inlet passage for the raw gas.

Fig. 2 shows a cross-section through various embodiments of the cyclone comprising different head portions as well as a different type of gas outlet tube and conical settling chamber.

In Fig. 1 picture la represents a cross-section of the cyclone. The cyclone comprises a head portion 1, a cylindrical separating chamber 2 and a two-part conical settling chamber with a different conicity (angles 131 and 132) of the two parts 3a, 3b. The dust-laden raw gas flows into the cylindrical separating chamber 2 through the inlet passage 4 via the inlet 5. The cleaned gas leaves the separating chamber 2 through the gas outlet tube 6 with the diameter D1. The gas outlet tube 6 is provided with a shielding cone 7. Picture lb shows the rectangular inlet cross-section 8 of the raw gas with a ratio between height H1 and width B1 of 4:1. Picture Ic shows a top view of the rectangular inlet passage 4. The inlet passage 4 can be parallel (broken line) or So° have a conicity, i.e. an angle a of 00 to 100. The ratio of the height H2 to the S• 20 diameter D2 of the cylindrical separating chamber 2 is 1:1. The point of entrance in the gas outlet tube is arranged between two points. The first point is 000* at a distance A below the head portion 1. The second point is at a distance B below the lowest point of the inlet cross-section 8. The line 9 for discharging solids is attached to the settling chamber 3a, 3b.

25 In Fig. 2 various embodiments of the head portion 1, the gas outlet tube 6 and the conical settling chamber 3 are represented. In Fig. 2a the cyclone 00 comprises a flat plate as head portion 1. The gas outlet tube 6 extends up to the 0@ 00 Smiddle of the inlet cross-section 8 for the taw gas and extends out of the conical settling chamber 3 in the shape of an arc. In Fig. 2b the cyclone comprises a dome-shaped head portion 1. In Fig. 2c the head portion 1 is dome-shaped.

00 The point of entrance into the gas outlet tube 6 lies at a distance C above the lowest point of the inlet cross-section 8 of the raw gas. A line 9 for discharging solids is attached to the conical settling chamber 3. In Fig. 2d the gas outlet tube 6 is straight and obliquely emerges from the conical settling chamber 3 with an angle between the longitudinal axis L1 of the gas outlet tube and the longitudinal axis L2 of the cyclone. The gas outlet tube 6 does not extend into the cylindrical separating chamber 2. Said cyclone has a ratio between height H2 and diameter D2 of the cylindrical separating chamber 2 of about 0.5:1. The point of entrance into the gas outlet tube 6 is arranged between two points. The first point is at a distance A below the head portion 1, while the second point is at a distance B below the lowest point of the inlet cross-section 8.

It was noted that the cyclone in accordance with the invention has an improved separation of solids as compared to a conventional cyclone. A further advantage in connection with gas streams having a high solids content is its resistance to "infiltrated air" due to the course of flow of such gas streams.

"Infiltrated air" is understood to be a stream of gas or air flowing through the line 9 for discharging solids into the cyclone, countercurrently to the solids discharged. Such streams of infiltrated air are produced in particular when a float chamber or a stationary fluidized bed are disposed below the cyclone. Part of the air used in these apparatuses for fluidizing the solids escapes through the line 9 for discharging solids, where it can entrain particles already separated in the cyclone and return them to the separating chamber 2. In addition, the stream of infiltrated air leads to a change in the pressure conditions in the separating chamber, which in general lead to a deterioration of the separating performance. Experiments with an inventive cyclone as compared to a conventional cyclone have shown that the embodiment in accordance with the invention has considerable advantages in the case of streams of infiltrated air, as they are usually produced in plants having a circulating fluidized bed.

Therefore, a preferred field of application of the cyclone in accordance with the invention is its use in plants including a circulating fluidized bed.

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6r 5 4O *5 8 In embodiments of the invention, the raw gas inlet is disposed in the lower half of the cylindrical separating chamber, that the height/diameter ratio of the cylindrical separating chamber lies in the range between 0.2:1 and 2.5:1, particularly 1.1:1 and 1.5:1, that the gas outlet tube protruding into the cyclone emerges laterally from the conical settling chamber or concentrically through a line for discharging solids, and that the point where the gas enters the gas outlet tube lies between two imaginary places, the lower one of which lies below the lowest point of the cross-section of the raw gas inlet and has a distance from the lowest point of the cross-section of the raw gas inlet which is up to twice the diameter of the gas outlet tube, and the upper one of which has a distance a from the head portion which is equal to once the diameter of the gas outlet tube.

Preferably, the distance from the lowest point is equal to twice the diameter of the gas outlet tube. Alternatively, the distance may be equal to the diameter of the gas outlet tube.

The term "cylindrical separating chamber" does not exclude that in this part of the cyclone there is already collected dust; the term "conical settling chamber" does not exclude that in this part of the cyclone there is still separated SIo. dust. It was noted that the cyclone in accordance with the invention leads to a #6 considerably improved separation of solids. The position of the raw gas inlet in 20 the lower half of the cylindrical separation chamber leads to the fact that there is 4P o, no secondary flow at the raw gas inlet, so that a short-circuit flow, which would let dust get into the clean gas stream, is largely avoided. The degree of separation of the cyclone furthermore depends on the rubbing surface of the conical settling chamber: The smaller the conicity (angle of inclination with respect to the vertical), the larger is the degree of separation. However, the o optimum angles of inclination depend on the properties of the material to be separated. An optimum angle of inclination can be determined by means of a few simple tests.

S° The embodiments have been advanced by way of example only and 30 modifications are possible within the spirit and scope of the invention as defined o. by the appended claims.

Claims (9)

1. A downflow cyclone for cleaning dust-laden gases and gaseous substances, the cyclone including: a closed head portion a cylindrical separating chamber arranged coaxially in relation to said head portion and located below said head portion, said cylindrical separating chamber having a height (H2) and a diameter (D2), a conical settling chamber arranged coaxially in relation to said separating chamber and located below said separating chamber, •o line for discharging solids from said settling chamber, said line *0 being located below said settling chamber, a raw gas inlet passage provided with an inlet opening to the 1cylindrical separating chamber said inlet opening having an inlet cross- section at said separating chamber, said inlet opening being positioned in the lower half of the cylindrical separating chamber and *a gas outlet tube protruding into an interior of the cyclone and having 9 a diameter (D1) and an entrance opening into which gas from the separating chamber enters the gas outlet tube; wherein said entrance opening is in an uppermost portion of said gas S: outlet tube located within said cyclone, said entrance opening is located between an upper theoretical horizontal plane and a lower theoretical horizontal plane, said upper theoretical horizontal plane is a first distance below the head portion said first distance being equal to the diameter (D1) of the gas outlet tube, and said lower theoretical horizontal plane is a second distance below a lowest point of said inlet cross-section said second distance being up to twice the diameter (D1) of the gas outlet tube a ratio of the height (H2) to the diameter (D2) of the cylindrical separating chamber is between 1.1:1 and 1.5:1, said gas outlet tube emerges laterally from the conical settling chamber or extends concentrically through said line for discharging solids, and said closed head portion consists of a flat plate.

2. The cyclone according to claim 1 wherein the second distance of the lower theoretical horizontal plane is equal to twice the diameter (D1) of the gas outlet tube

3. The cyclone according to claim 1 wherein the second distance of the lower theoretical horizontal plane is equal to the diameter (D1) of the gas outlet tube

4. The cyclone according to any one of claims 1 to 3, wherein the cross- section of the raw gas inlet is rectangular with a ratio between height H1 and width B1 in the range between 1:1 and 5:1. The cyclone according to any one of claims 1 to 4, wherein the conical settling chamber has a two-part design, comprising an upper, longer part (3a) with an angle of inclination 131 of 20 to 100 and a lower, shorter part (3b) with an angle of inclination 32 of 100 to 450. 0@

6. The cyclone according to any one of claims 1 to 5, wherein a shielding cone is disposed in the conical settling chamber

7. The cyclone according to any one of claims 1 to 6, wherein the raw gas flows into the cylindrical separating chamber through a spiral inlet, a slotted inlet, a tubular inlet, an axial inlet or a helical inlet.

8. The cyclone according to any one of claims 1 to 7, wherein the point Swhere the gas flows into the gas outlet tube is disposed in the conical settling chamber S.

9. The cyclone according to any one of claims 1 to 8, wherein the cyclone is o• used for cleaning dust-laden gases and gaseous substances. 5' 11 The cyclone according to any one of claims 1 to 9, wherein the cyclone is used as a recirculating cyclone in plants comprising a circulating fluidized bed.

11. A downflow cyclone for cleaning dust-laden gases and gaseous substances substantially as hereinbefore described and illustrated with reference to the accompanying drawings. DATED this 1st day of March, 1999 METALLGESELLSCHAFT AKTIENGESELLSCHAFT WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA SKP:RJS:PCP Doc 24 AU 4815796.WPC s CC*C Cg 00