GB2066685A

GB2066685A - Handling fine dusts without pollution

Info

Publication number: GB2066685A
Application number: GB7944149A
Authority: GB
Original assignee: Bergsoe & Son As P
Current assignee: Bergsoe & Son As P
Priority date: 1979-12-21
Filing date: 1979-12-21
Publication date: 1981-07-15

Abstract

Fine metallurgical dusts, possibly toxic, are separated from air in a venturi scrubber or in a dry filter from which they are discharged into water. The resulting water-dust mixtures are filtered to produce cake, which is bonded by adhesive such as glue, sulphite lye, lignosulphate compounds or polyvinyl acetate. The adhesive is either mixed with the water used in the scrubber or on the discharge side of the dry filter or alternatively is pumped through the filter after the filtration stage. The resulting cake is discharged from the filter and formed into flat slabs, which are then heated to harden their surfaces sufficiently to allow mechanical handling.

Description

SPECIFICATION An improved method for handling fine dusts without pollution We, Paul Bergsoe & Sen A/S, a Danish company of Hvissingevej 100,2600 Glostrup, Denmark, 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 as described in the following statement.

Dust is produced in a wide variety of industrial processes and is frequently a source of atmospheric pollution in the area surrounding that in which the process is operated. In the metallurgical industry in particular, a common operation is smelting in which compounds of a particular metal, such as its oxide or sulphide, are reduced to the metallic state. Smelting is nearly always carried out at elevated temperatures in furnaces of a wide variety, and at these elevated temperatures it is common that some vaporisation lof the metal and/or metal compounds occurs. Once the vapours leave the furnace and cool down, condensation occurs with the production of a fine dust often of sub-micron particle size.

Severe problems occur in some smelting plants due to the toxic nature of the dust produced, which commonly has an appreciable intrinsic value due to the amount of metal contained in it. To prevent pollution of the surrounding areas and to recover the dust in order to process it for recovery of its metal value, it is necessary to filter the gases exhausted from the furnaces to remove the dust particles prior to discharging the gases to the atmosphere. Having recovered the dust particles with the use of a wide variety of gas filtration processes, problems arise due to the fact that dusts of very fine particle size are readily assimilated into the bodies of plant operators via their digestive or respiratory systems, and if such dusts are toxic, poisoning can readily occur.The handling of such toxic materials as a prerequisite to reprocessing them in any manner in which ingestion into the human system can occur is therefore very dangerous.

Where such dusts have a relatively low melting point, such as those produced in the secondary lead smelting industry, the problem of handling the fine toxic dust can be overcome by the means described in Danish Patent No. 132900of26thJu1y, 1979,the corresponding United States Patent No. 4013466 of 22nd March, 1977 and in the corresponding British Patent No.1 51 555 of 9th June, 1975. However, many dusts are not amenable to such treatment and it is then common to render the dust less hazardous to handle by thoroughly wetting it. This can be achieved either by discharging the dust into water directly from the filter if collected in a dry condition, or by use of such equipment as a venturi scrubber or disintegrator in which water is used as the medium to collect the fine dust particles.It is then common to filter the solid/liquid mixture using a filter press or similar equipment to recover the solids in a damp form.

Unfortunately the dampness is only of temporary nature unless water is repeatedly added at frequent intervals, as evaporation of water into the atmosphere returns the solid dust particles to their previous hazardous nature. It is the object of this invention to prevent the dust returning to a hazardous nature.

This is achieved by using an aqueous solution of a certain chemical reagent, instead of water, as the medium in which the individual particles of dust are immersed. After filtration each particle of dust is coated with a solution of the reagent, and on standing exposed to the atmosphere the moisture evaporates leaving each particle coated with a thin layer of the reagent itself. Such reagents must have properties such that the coating on one particle will adhere firmly to the coating on any other, thus cementing the particles into a dustless lump form. Suitable chemical reagents are typically, but not limited to, animal glue, water-soluble or water-dispersible adhesives such as polyvinyl acetate, and lignosulphate compounds, commonly known as sulphite lye.

Should for any reason introducing the binding agent into the bulk of water in the collection circuit be found to be objectionable, filtration of the solids/water mixture can proceed in the normal manner, but prior to discharging the filter cake, a solution of the particular chemical reagent can be pumped through the cake whilst still in the filter from a separate small reservoir for sufficient time to introduce the reagent into the interstices between the solid particles. The filter cake is then discharged in the normal manner.

In a preferred embodiment of the process, the solids after discharge from the filter are shaped into a flat layer 1-2 cms in thickness and gentle heat applied to the surface layers in order to raise the temperature of the outer 1 millimetre thick layers to a temperature of minimum 110 C and maximum 1 500C. The effect of this heating operation, akin to toasting, is to evaporate the water in the surface layers producing an immediate hardness, but by limiting the maximum temperature to 1 500C, water is not evolved from the interior in the form of steam at such a rate that disintegration of the biscuit occurs.

Sufficient strength is however developed to permit handling by conventional mechanical handling equipment.

1. An improved method for handling fine dusts, particularly of a toxic nature, characterised by collecting the dust in an aqueous solution of a binding agent of sufficient strength that after filtration each particle of dust is coated with a layer of the binding agent which will adhere firmly to adjacent particles to produce a firm, solid agglomerate after evaporation of the moisture content.

2. An improved method for handling fine dusts, particularly of a toxic nature, characterised by collecting the dust in water, filtering the solid/liquid mixture so obtained, but prior to discharging the cake of solids from the filter, impregnating the cake with an aqueous solution of a binding agent so that on discharge the solids possess the same properties as described in Claim 1.

3. A method as described in either Claims 1 or2, in which the preferred binding agent is sulphite lye.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION An improved method for handling fine dusts without pollution We, Paul Bergsoe & Sen A/S, a Danish company of Hvissingevej 100,2600 Glostrup, Denmark, 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 as described in the following statement. Dust is produced in a wide variety of industrial processes and is frequently a source of atmospheric pollution in the area surrounding that in which the process is operated. In the metallurgical industry in particular, a common operation is smelting in which compounds of a particular metal, such as its oxide or sulphide, are reduced to the metallic state. Smelting is nearly always carried out at elevated temperatures in furnaces of a wide variety, and at these elevated temperatures it is common that some vaporisation lof the metal and/or metal compounds occurs. Once the vapours leave the furnace and cool down, condensation occurs with the production of a fine dust often of sub-micron particle size. Severe problems occur in some smelting plants due to the toxic nature of the dust produced, which commonly has an appreciable intrinsic value due to the amount of metal contained in it. To prevent pollution of the surrounding areas and to recover the dust in order to process it for recovery of its metal value, it is necessary to filter the gases exhausted from the furnaces to remove the dust particles prior to discharging the gases to the atmosphere. Having recovered the dust particles with the use of a wide variety of gas filtration processes, problems arise due to the fact that dusts of very fine particle size are readily assimilated into the bodies of plant operators via their digestive or respiratory systems, and if such dusts are toxic, poisoning can readily occur.The handling of such toxic materials as a prerequisite to reprocessing them in any manner in which ingestion into the human system can occur is therefore very dangerous. Where such dusts have a relatively low melting point, such as those produced in the secondary lead smelting industry, the problem of handling the fine toxic dust can be overcome by the means described in Danish Patent No. 132900of26thJu1y, 1979,the corresponding United States Patent No. 4013466 of 22nd March, 1977 and in the corresponding British Patent No.1 51 555 of 9th June, 1975. However, many dusts are not amenable to such treatment and it is then common to render the dust less hazardous to handle by thoroughly wetting it. This can be achieved either by discharging the dust into water directly from the filter if collected in a dry condition, or by use of such equipment as a venturi scrubber or disintegrator in which water is used as the medium to collect the fine dust particles.It is then common to filter the solid/liquid mixture using a filter press or similar equipment to recover the solids in a damp form. Unfortunately the dampness is only of temporary nature unless water is repeatedly added at frequent intervals, as evaporation of water into the atmosphere returns the solid dust particles to their previous hazardous nature. It is the object of this invention to prevent the dust returning to a hazardous nature. This is achieved by using an aqueous solution of a certain chemical reagent, instead of water, as the medium in which the individual particles of dust are immersed. After filtration each particle of dust is coated with a solution of the reagent, and on standing exposed to the atmosphere the moisture evaporates leaving each particle coated with a thin layer of the reagent itself. Such reagents must have properties such that the coating on one particle will adhere firmly to the coating on any other, thus cementing the particles into a dustless lump form. Suitable chemical reagents are typically, but not limited to, animal glue, water-soluble or water-dispersible adhesives such as polyvinyl acetate, and lignosulphate compounds, commonly known as sulphite lye. Should for any reason introducing the binding agent into the bulk of water in the collection circuit be found to be objectionable, filtration of the solids/water mixture can proceed in the normal manner, but prior to discharging the filter cake, a solution of the particular chemical reagent can be pumped through the cake whilst still in the filter from a separate small reservoir for sufficient time to introduce the reagent into the interstices between the solid particles. The filter cake is then discharged in the normal manner. In a preferred embodiment of the process, the solids after discharge from the filter are shaped into a flat layer 1-2 cms in thickness and gentle heat applied to the surface layers in order to raise the temperature of the outer 1 millimetre thick layers to a temperature of minimum 110 C and maximum 1 500C. The effect of this heating operation, akin to toasting, is to evaporate the water in the surface layers producing an immediate hardness, but by limiting the maximum temperature to 1 500C, water is not evolved from the interior in the form of steam at such a rate that disintegration of the biscuit occurs. Sufficient strength is however developed to permit handling by conventional mechanical handling equipment. CLAIMS

4. A method as described in any of Claims 1-3 inclusive in which gentle heat is applied to the surface layer of the filter cake produces ~O give a temperature in the outer surface layer of 1 millimetre thickness of minimum 1 100C and maximum 1500C in order to facilitate handling by conventional mechanical handling equipment.

5. The improved method for handling fine dusts substantially as hereinbefore described.