Title of Invention

A PROCESS FOR PRODUCING A HEAVY MEDIUM FOR COAL WASHERIES.

Abstract

The invention provides ess for producing a heavy medium for coal washeries, using mill scale and blast furnace flue dust mixture generated in integrated steel plants. It comprises the steps of screening the mill scale for its size, grinding the mill scale to have a size of less than 0.044 mm; subjecting the blast furnace flue dust to dry magnetic separation to generate a magnetic fraction of desired specific gravity; mixing the magnetic fraction of the flue dust with the ground mill scale to make a homogenous mixture of desired specific gravity, grinding the mixture to have at least 90% in size of less than 0.045 mm and adding required amount of water to the ground mixture for making a heavy medium of the desired specific gravity of suspension for use in lcoal washeries.

Full Text

This invention relates to a process for producing heavy medium for coal washeries, using millscale and blast furnace flue dust mixture generated in integrated steel plants. It is known that the coarse fraction of non oily millscale, generally called millscale (about +1 mm and having oil content 2%) is presently being used in sinter plants and blast furnaces. The flue dust (rich in alkali) is now discarded as waste. In the manufacture of blast furnace coke from coal, the coal is subjected to washing for lowering the ash content so that the high ash Indian coal can be usefully employed in coke manufacture. The ash content is to be lowered to a practical limit of 17-18% which is dictated by the quality of Indian coking coals. The general practice of coal washing is to crush the coal to below 50 mm or less, followed by separate treatment of coarse (+0.5mm) and fine (-0.5 mm) coal fractions. While fine coal is processed by froth flotation, coarse coal cleaning is universally carried out by heavy medium separation. In commercial plants of heavy medium separation using dense medium cyclones, finely divided solids of magnetite are kept in suspension in water to create a dense medium. Thus for the creation of the heavy medium in the above mentioned coal washing procedure, magnetite is being employed. In India, the reserves of magnetite material are meagre and therefore an alternative source of heavy medium for use in coal washeries has assumed importance. It is already known to use secondary magnetite obtained as a by-product in the plants for uranium ore extraction, as heavy medium in coal washeries. However, the qualities, properties and the cost of secondary magnetite now vary considerably and therefore, a uniform variety of secondary magnetite has become essential. Moreover, since the coal industry in India is ever expanding, the demand for secondary magnetite has assumed huge proportions. If the magnetite requirements of the coal washeries can be shifted from the mineral magnetite to other secondary sources of substantially similar qualities, not only a great saving of the magnetite can be ensured for other more important and useful purposes, but also a secondary source can be beneficially developed. It is therefore, an object of this invention to propose a process for the utilization of millscale + flue dust mixture as heavy medium in coal washeries. It is another abject of this invention to propose such a process which will produce substantially uniform quality of a material alternative to magnetite. It is a further object of this invention to propose a process which will be economical and can be practised without difficulty. A stil further object of the present invention is to propose such a process by which the degree of pollution contributed by millscale and blast furnace flue dust can be controlled or removed due to its usage as heavy medium in coal washing plants. Thus according to this invention, there is provided a process for producing a heavy medium for coal washeries, using millscale and blast furnace flue dust mixture generated in integrated steel plants, comprising the steps of screening the millscale for its size; grinding the millscale to have a size of less than 0.044 mm; subjecting the blast furnace flue dust to magnetic separation to generate a magnetic fraction of desired specific gravity; mixing the magnetic fraction of said flue dust with said ground millscale to make a homogenous mixture of desired specific gravity; grinding the mixture to have at least 90% in size of less than 0.049 mm; and adding required amount of water to the ground mixture for making a heavy medium of the desired specific gravity of suspension, for use in coal washeries. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description. The mill scale + flue dust contains magnetic property and hence compares closely with magnetite, which is generally mined and used as heavy medium in coal washeries. The description that follows also show that the properties of mill scale + flue dust compare favourably with those of magnetite. It will be seen that the properties of mill scale + flue dust and magnetite are almost identical, but for minor differences. It has been found that the mill scale + flue dust can be gainfully employed as heavy medium in conventional coal washing industries. The process of manufacture of blast furnace coke from coal has been discussed in detail in pages 2 and 3. Table 1 shows a comparison between the millscale + flue dust and magnetite which indicates size is 90% below 0.045 mm compared to 80% below for magnetite. Stability and recoverability is also better in case of millscale + flue dust. Table 2 compares results of the dense media cyclone tests which indicates a better clean coal yield in case of millscale + flue dust used as heavy medium. The process steps will now be described in detail. The coarse and non oily millscale generated in the steel plant is screened and particles of size bigger than 0.044mm are ground to reduce to sizes below 0.044 mm. The blast furnace flue dust from the steel plant is then subjected to dry magnetic separation to get a magnetic product. The magnetic separation is carried out at 7000 gauss to generate a magnetic fraction of specific gravity 3. The magnetic product thus obtained from bast furnace flue dust is then mixed homogenously with the ground millscale, at least 90% of the latter being of size less than 0.044 mm. The mixing can be carried out in the ratio of 47 parts of magnetic product to 53 parts of ground millscale for obtaining a product specific gravity not less than 4.5. The mixture is then ground to get a product with more than 90% passing through 0.045 mm. Desired amount of water is then added to this mixture for making the desired specific gravity of suspension. This material can then be used as heavy medium in coal washeries. The recoverability is 85% at 7000 gauss. The percentage of clean coal yield is 4.81 to 26.33 depending on clean coal ash percentage of 5.74 to 13.58 as shown in Table - 2. The invention herein described should be considered am illustrative and not as restrictive. It is to be appreciated that those skilled in the art can make changes or modifications without departing from the scope and spirit of the invention. WE CLAIM: 1. A process for producing a heavy medium for coal washeries, using millscale and blast furnace flue dust mixture generated in integrated steel plants, comprising the steps of: - screening the millscale for its size; - grinding the millscale to have a size of less than 0.044 mm; - subjecting the blast furnace flue dust to magnetic separation at 7000 gauss to generate a magnetic fraction of desired specific gravity; - mixing the magnetic fraction of said flue dust with said ground millscale to make a homogenous mixture of desired specific gravity; - grinding the mixture to have at least 90% in size of less than 0.045 mm; and - adding required amount of water to the ground mixture for making a heavy medium of the desired specific gravity of suspension, for use in coal washeries. 2. A process for producing a heavy medium for coal washeries as claimed in claim 1, wherein the specific gravity of said magnetic fraction generated is 3. 3. A process for producing a heavy medium for coal washeries as claimed in claims 1 and 2, wherein the step of mixing said magnetic fraction of flue dust with said ground millscale is carried out in the ratio 47:53 to make a homogenous mixture of specific gravity not less than 4.5. 4. A process for producing a heavy medium for coal washeries substantially as herein described. The invention provides ess for producing a heavy medium for coal washeries, using mill scale and blast furnace flue dust mixture generated in integrated steel plants. It comprises the steps of screening the mill scale for its size, grinding the mill scale to have a size of less than 0.044 mm; subjecting the blast furnace flue dust to dry magnetic separation to generate a magnetic fraction of desired specific gravity; mixing the magnetic fraction of the flue dust with the ground mill scale to make a homogenous mixture of desired specific gravity, grinding the mixture to have at least 90% in size of less than 0.045 mm and adding required amount of water to the ground mixture for making a heavy medium of the desired specific gravity of suspension for use in coal washeries.

Documents:

00506-kol-2003-abstract.pdf

00506-kol-2003-claims.pdf

00506-kol-2003-correspondence.pdf

00506-kol-2003-description (complete).pdf

00506-kol-2003-form 1.pdf

00506-kol-2003-form 18.pdf

00506-kol-2003-form 2.pdf

00506-kol-2003-form 26.pdf

00506-kol-2003-form 3.pdf

00506-kol-2003-letter patent.pdf

00506-kol-2003-reply f.e.r.pdf