GB1564710A

GB1564710A - Method and apparatus for eliminating solids from gas exhausted from a dryer drum in which a mixture containing bituminous binding material is processed

Info

Publication number: GB1564710A
Application number: GB47639/76A
Authority: GB
Original assignee: Wibau GmbH
Current assignee: Wibau GmbH
Priority date: 1976-01-20
Filing date: 1976-11-16
Publication date: 1980-04-10
Also published as: DK405676A; ZA764926B; FR2339019A1

Description

(54) METHOD AND APPARATUS FOR ELIMINATING SOLIDS FROM GAS EXHAUSTED FROM A DRYER DRUM IN WHICH A MIXTURE CONTAINING BITUMINOUS BINDING MATERIAL IS PROCESSED (71) We, WIBAU (WESTDEUTSCHE INDUSTRIE-UND STRAssENBAU- MASCHINEN GMBH), a German Company of Wibaustrasse 1, 6466, Grundau-Rothenbergen, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to the cleaning of exhaust gases from a dryer drum in which a bituminous binding material mixed with preferably mineral solid materials of different grain size is dried and processed to form a bituminous mixture.

German Patent Specification No.

1,594,815 discloses mixing of non-dried solid materials with the liquefied binding material and a subsequent mixing under application of strong heat. The finest particles initially cling to the coarser granules by the water film, and in the course of the processing, i.e.

when the water is evaporated, the binding of these particles is taken over by the binding material, which flows at the high temperatures used. The binding material droplets sticking to the granules are converted during the process into very thin films covering the individual particles. It was originally expected that the emission of dust would be practically eliminated, leading to the possibility of abandonment of the usual dust arrester installation, but this was not always achieved. The dust emission found in practice is, it is true, only 3 to 10% of the normal emission of a drum dryer, which, however, nowadays in view of the increasing requirements of environmental protection is no longer adequate.

It has been found that the form and intensity of the dust emissions are primarily dependent not on the mixing and drying procedure or the design of the individual drum dryer system, but on the type of mixture to be produced, the minerals being used, the particle size and moisture content and the type of binding material. Only in very rare cases does identical equipment show, when the site is changed, absolutely identical values in mixture capacity and exhaust gas characteristics.

Pollutant dust arises from the solids being mixed; gaseous and aerosol pollutants arise from the binder.

The present invention resides in a method of separating pollutants from exhaust gases from a dryer drum in which a mixture containing bituminous binding material and particulate solid material is dried and processed to form a bituminous mixture, in which method the exhaust gases laden with pollutants are conducted through at least one flat filter element having a granulated or fibrous filling and disposed in the suction head of the dryer which head is constructed to form a separation vessel and the filter element is or elements are cleaned at intervals by shaking and/or rinsing until the flow resistance thereof is reduced to a preset minimum.

The invention also resides in a drum dryer for mixing bituminous binder with solid material, which comprises a suction head constituting a separation vessel mounted at the outlet of the dryer drum and provided with a gas outlet, at least one flat filter element in the gas flow path from the dryer drum to the gas outlet, means for cleaning the filter element(s) by shaking and/or rinsing, means for returning separated solid material from the separation vessel to the dryer drum, and control means arranged to actuate the cleaning means at intervals and thereby to reduce the flow resistance of the filter element(s) to a preset minimum.

With the invention, an emission of 0.08 to 1.5 g/m3 can be obtained whereas when utilising the prior art procedures the emission is normally about 40 to 120 g/m3.

Naturally, with these efforts no linearity of the results can be expected; the reduction of an emission already tending to zero is and remains more expensive than the reduction of a peak emission.

The exhaust fumes conducted through the separating vessel may be treated additionally by baffle plates therein.

The filter elements are preferably exchangeable and selectable or adjustable in regard to their filling level, the type of the filling material and its grain size.

Advantages resulting from this solution of the problem include: 1. Possibility to adapt the separation system, starting from the simplest up to high quality filter elements, which if required could absorb gaseous impurities.

2. Use of filter material which is not sensitive to overheating nor to conditions below dew-point.

3. The possibility to water-spray the filter elements on the clear side to condense noxious gases, and to assist mechanical filter element cleaning.

4. Return of the solid material separated into the mixture and its melting into the mixture stream without any risk.

For the sake of easy handling when changing the filter elements and to enable this change to be performed in steps, i.e.

section by section, it is preferred that the exhaust gases conducted through the separation vessel are guided through a flat filter assembly consisting of several, individually exchangeable filter elements.

The filter elements are preferably filled with rock, coke, activated carbon, metal oxides or other absorbing or reducing materials, essentially of a granular and/or fibrous structure, an element either containing just one of these materials or a mixture of one or more materials.

With this proposal not only is it possible to combine the filter materials in each individual case to attain optimal efficiency, but at the same time it is to be pointed out that by suitable selection of the filter material or materials any particular pollutants can be eliminated from the exhaust gas. Furthermore the saturated filter material could be recycled to the dryer drum for incorporation in the bituminous mixture.

Since the efficiency of separation of a filter largely depends on the gas speed it is preferred that the speed of the exhaust in the separation vessel is reduced about 50% more morn compared with its speed in the - intorlale s +: from which the time taken to read a predetermined maximum flow resistance can be determined. The intervals at which the cleaning has to be repeated will normally be kept slightly shorter than the time thus determined, and the control means will be programmed accordinglv.

The filter elements or their filling will be cleaned at the predetermined intervals by shaking and/or rinsing until a pre-set minimum flow resistance is reached. When this value is reached an inpulse is given for beginning the next interval, for instance by activating a pre-settable time relay, and when the selected period of time has run out the cleaning process is repeated.

Instead of setting fixed time intervals, it can be arranged that the impulse for starting the cleaning of the filter elements is given when a predetermined maximum flow resistance has been reached and, as already proposed the filter element is cleaned until the minimum flow resistance is reached.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 shows a drum dryer suction head fitted with plate filter elements; Figure 2 shows equipment as in Figure 1, equipped in addition with liquid spray nozzles; Figure 3 shows a partial section through a filter element with a coke filling; and Figure 4 shows a section through an individual filter element.

The hatched arrows show the path of the solid materials. The open arrows mark the path of the exhaust gases.

The end of a drum layer outlet pipe 1 extends into the suction head 2, which has a removable top 3 and constitutes a separation vessel, and can be equipped with different forms of separation equipment and has on its clean gas side the exhaust gas suction outlet 13.

By a wall 12 the vessel 2 is divided into an outlet region with a solids outlet 14, and a dust collection region. The material separated from the exhaust gases is conducted by a screw into the outlet region and then through outlet 14.

Impact with the wall 12 causes separation of dust from the gases. This dust falls to the bottom of the collection region and is conveyed by conveyor screw 4 to the outlet 14, whence it is returned to the dryer drum.

Baffle plates can be attached to the removable top 3 in any convenient way, or can be mounted in channels on or in the side walls of the vessel.

The top 3 is provided with transverse inverted T-section bars 5 for supporting desired be provided in addition to the filter elements 7. Access to the baffle plates and/or filter elements 7 is provided by removing the top 3 from the separation vessel. To facilitate filter changing, the flanges of bars 5 may be provided with wheels or rollers, and the bars may have stops and/or catches for locating the filter elements.

As shown in Figures 3 and 4, the filter element 7 consists of a lower mesh, grid, perforated plate 8 or the like, a perforate upper member 9, and a frame 10, on which the lower member 8 is placed, and a 0.1 m thick coke layer 11.

The diameters or cross-sections of the holes in the upper filter member 9 are reduced in comparison to those in the lower filter member 8.

A filter element with a layer thickness of 0.1 m and a filter surface of 1 by 1.5 m and a weight of about 140 kg. can handle the exhaust gases arising when about 150 kg/h of fuel oil are burnt.

The top 3 is fitted with one or more pipes 15 providing an array of spray nozzles arranged to spray water onto the upper surfaces of the filter elements 7, as shown in Figure 2. The nozzles are arranged to spray the whole upper surface of the filter elements, for cleaning these at intervals as described above.

WHAT WE CLAIM IS: 1. A method of separating pollutants from exhaust gases from a dryer drum in which a mixture containing bituminous binding material and particulate solid material is dried and processed to form a bituminous mixture, in which method the exhaust gases laden with pollutants are conducted through at least one flat filter element having a granulated or fibrous filling and disposed in the suction head of the dryer which head is constructed to form a separation vessel, and the filter element is or elements are cleaned at intervals by shaking and/or rinsing until the flow resistance thereof is reduced to a preset minimum.

2. A method according to Claim 1 in which the exhaust gases conducted through the separation vessel are cleaned therein by contact with baffle plates as well as by the filter element(s).

3. A method as claimed in Claim 1 or 2 in which the solid material separated from the exhaust gases in the separation vessel is returned to the dryer drum.

4. A method as claimed in Claim 1, 2 or 3 the filter element(s) being exchangeable and selectable or adjustable as to filling level, the type of filling material and the filling grain size.

5. A method according to any preceding claim characterised by the fact that the exhaust gases while being conveyed through the separation vessel are guided through a filter assembly consisting of several, individually exchangeable filter elements.

6. A method according to any preceding claim characterised by the fact that the filter element is or filter elements are filled with rock, coke, activated carbon, metal oxides or other absorbing or reducing materials essentially of a granulated and/or fibrous structure, each element containing a single material or a mixture of one or more materials.

7. A method according to any preceding claim characterised by the fact that the speed of the exhaust gases in the separation vessel, compared with the speed in the dryer drum, is reduced by about 50% or more.

8. A method according to any preceding claim characterised by the fact that a starting impulse for the cleaning of the filter element(s) is given when a predetermined maximum flow resistance has been reached.

9. A method according to any of Claims 1 to 7 in which the cleaning of the filter element(s) is performed at predetermined time intervals.

10. A drum dryer for mixing bituminous binder with solid material, which comprises a suction head constituting a separation vessel mounted at the outlet of the dryer drum and provided with a gas outlet, at least one flat filter element in the gas flow path from the dryer drum to the gas outlet, means for cleaning the filter element(s) by shaking and/or rinsing, means for returning separated solid material from the separation vessel to the dryer drum, and control means arranged to actuate the cleaning means at intervals and thereby to reduce the flow resistance of the filter element(s) to a preset minimum.

Il. A drum dryer as claimed in Claim 10 including at least one liquid spray nozzle mounted in the vessel and arranged to spray liquid on the filter element(s).

12. A drum dryer as claimed in Claim 10 or 11 in which the top of the vessel is removable for access to the filter element(s).

13. A drum dryer as claimed in Claim 12 when dependent on Claim 11, wherein the spray nozzle is or nozzles are mounted in the removable top of the vessel.

14. A drum dryer as claimed in Claim 10, 11, 12 or 13 in which the or each filter element is removable.

15. A drum dryer as claimed in any of Claims 10 to 14 in which the separation vessel is provided with at least one baffle plate in the gas flow path.

16. A drum dryer for mixing bituminous

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

desired be provided in addition to the filter elements 7. Access to the baffle plates and/or filter elements 7 is provided by removing the top 3 from the separation vessel. To facilitate filter changing, the flanges of bars 5 may be provided with wheels or rollers, and the bars may have stops and/or catches for locating the filter elements.

As shown in Figures 3 and 4, the filter element 7 consists of a lower mesh, grid, perforated plate 8 or the like, a perforate upper member 9, and a frame 10, on which the lower member 8 is placed, and a 0.1 m thick coke layer 11.

The diameters or cross-sections of the holes in the upper filter member 9 are reduced in comparison to those in the lower filter member 8.

A filter element with a layer thickness of 0.1 m and a filter surface of 1 by 1.5 m and a weight of about 140 kg. can handle the exhaust gases arising when about 150 kg/h of fuel oil are burnt.

The top 3 is fitted with one or more pipes

15 providing an array of spray nozzles arranged to spray water onto the upper surfaces of the filter elements 7, as shown in Figure 2. The nozzles are arranged to spray the whole upper surface of the filter elements, for cleaning these at intervals as described above.

WHAT WE CLAIM IS: 1. A method of separating pollutants from exhaust gases from a dryer drum in which a mixture containing bituminous binding material and particulate solid material is dried and processed to form a bituminous mixture, in which method the exhaust gases laden with pollutants are conducted through at least one flat filter element having a granulated or fibrous filling and disposed in the suction head of the dryer which head is constructed to form a separation vessel, and the filter element is or elements are cleaned at intervals by shaking and/or rinsing until the flow resistance thereof is reduced to a preset minimum.
2. A method according to Claim 1 in which the exhaust gases conducted through the separation vessel are cleaned therein by contact with baffle plates as well as by the filter element(s).
3. A method as claimed in Claim 1 or 2 in which the solid material separated from the exhaust gases in the separation vessel is returned to the dryer drum.
4. A method as claimed in Claim 1, 2 or 3 the filter element(s) being exchangeable and selectable or adjustable as to filling level, the type of filling material and the filling grain size.
5. A method according to any preceding claim characterised by the fact that the exhaust gases while being conveyed through the separation vessel are guided through a filter assembly consisting of several, individually exchangeable filter elements.
6. A method according to any preceding claim characterised by the fact that the filter element is or filter elements are filled with rock, coke, activated carbon, metal oxides or other absorbing or reducing materials essentially of a granulated and/or fibrous structure, each element containing a single material or a mixture of one or more materials.
7. A method according to any preceding claim characterised by the fact that the speed of the exhaust gases in the separation vessel, compared with the speed in the dryer drum, is reduced by about 50% or more.
8. A method according to any preceding claim characterised by the fact that a starting impulse for the cleaning of the filter element(s) is given when a predetermined maximum flow resistance has been reached.
9. A method according to any of Claims 1 to 7 in which the cleaning of the filter element(s) is performed at predetermined time intervals.
10. A drum dryer for mixing bituminous binder with solid material, which comprises a suction head constituting a separation vessel mounted at the outlet of the dryer drum and provided with a gas outlet, at least one flat filter element in the gas flow path from the dryer drum to the gas outlet, means for cleaning the filter element(s) by shaking and/or rinsing, means for returning separated solid material from the separation vessel to the dryer drum, and control means arranged to actuate the cleaning means at intervals and thereby to reduce the flow resistance of the filter element(s) to a preset minimum.
Il. A drum dryer as claimed in Claim 10 including at least one liquid spray nozzle mounted in the vessel and arranged to spray liquid on the filter element(s).
12. A drum dryer as claimed in Claim 10 or 11 in which the top of the vessel is removable for access to the filter element(s).
13. A drum dryer as claimed in Claim 12 when dependent on Claim 11, wherein the spray nozzle is or nozzles are mounted in the removable top of the vessel.
14. A drum dryer as claimed in Claim 10, 11, 12 or 13 in which the or each filter element is removable.
15. A drum dryer as claimed in any of Claims 10 to 14 in which the separation vessel is provided with at least one baffle plate in the gas flow path.
16. A drum dryer for mixing bituminous

binder with solid material, substantially as herein described with reference to the accompanying drawings.