Claims:We Claim:
1. A system for segregation of low ash clean coal from coal tailings comprising
at least one crushing mill or crusher configured for grinding coal tailing to a pre-determined size;
at least one water source to feed water at various stages of the process of segregation of low ash clean coal from coal tailings; and
at least one centrifuge configured to be operated at different speeds for separation of different types of coal.

2. The system as claimed in claim 1 wherein said coal tailing is configured to be fed to crushing mill or crusher along with water to form coal slurry for maintaining pre-determined coal to water ratio.

3. The system as claimed in claim 1 wherein said at least one crushing mill or crusher is a planetary ball mill configured for forming ultrafine sized coal water slurry.

4. The system as claimed in claim 1 wherein said coal tailings are configured to be grinded in said crushing mill or crusher to a particle size of less than 45 microns.

5. The system as claimed in claim 1 wherein said high-speed centrifuged operated at different speeds is configured to separate said ultrafine sized coal water slurry in three different layers viz first (top) layer is mainly water along with nano sized carbon particles; second (middle) layer of low ash coal is soft coal slurry at lower ash levels and third (bottom) layer is a hard coal at higher ash level.

6. The system as claimed in claim 1 wherein said second layer of low ash coal is configured to be removed from the centrifuge by scrapping out and discharging it at a predetermined level.

7. The system as claimed in claim 1 wherein said third layer of high ash coal layer is configured to be separated from the centrifuge by scrapping from the walls of the centrifuge for its separation.

8. The system as claimed in claim 1 wherein said centrifugation for separation of low ash coal is configured to be carried out in a speed range of 2,000 rpm -10,000 rpm to improve the separation efficiency.

9. The system as claimed in claim 1 wherein said centrifuge is configured for recovering total carbon of 75-84.5% in clean coal with 43.8-47.2% moisture, specific gravity of 1.28 and calorific value of 21.92-24.4 MJ/kg, suitable for coke making application.

10. The process of separation of low ash clean coal from coal tailings comprising the steps of:
• feeding of tailing coal in the crushing mill or crusher along with water for fine and homogenous grinding of coal tailing to a particle size of less than 45 microns and to produce feed coal slurry with a pulp density of 1:1 ratio;
• mixing water in the coal slurry to maintain required coal to water ratio before feeding it to centrifuge to improve particle-particle interaction for good separation;
• feeding the water and coal slurry mixture in a high-speed centrifuge operated at differential speeds for separation of the water and coal slurry mixture into different layers of high ash coal layer, low ash coal layer and water to get an average coal ash of 14.8%-16.4% with 58.5 to 68.9% yield for a feed coal ash of 34.9%;
• removing layer of low ash coal from the centrifuge by scrapping out and discharging it at a predetermined level; and
• removing layer of high ash coal from the centrifuge by scrapping it from the walls of the centrifuge for its separation.

Dated 05th day of February 2020

Gopinath Arenur Shankararaj
IN/PA 1852
OF K&S PARTNERS
AGENT FOR THE APPLICANT
, Description:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

Title of the subject matter:
A SYSTEM AND PROCESS FOR SEGREGATION OF LOW ASH CLEAN COAL FROM COAL TAILINGS

Name and address of the Applicant:

TATA STEEL LIMITED, Jamshedpur, Jharkhand, India 831001

And

INDIAN INSTITUTE OF TECHNOLOGY, HYDERABAD, Near NH-65, Sangareddy,
Khandi, Hyderabad, Telangana Pin -502285

Nationality: INDIAN

The following specification describes the subject matter and the manner in which it is to be performed.
Field of Invention
[001] The subject matter of the present disclosure is of coal and more particularly it describes about the separation of low ash coal from tailings coal.

Background of Invention
[002] Metallurgical grade coal is a primary raw material for iron and steel making process through blast furnace route. Metallurgical coal or coking coal is a grade of coal that can be used to produce good-quality coke. Metallurgical coal is low in ash, moisture, sulfur and phosphorus content, and is usually of Bituminous rank. Quality of final product depends merely on the quality of raw coal, where ash content of the coal has a major impact. Present iron and steel making process utilizes coal at an ash level ranging 15-18.5%. However, Indian run of mine coals are of high ash grade, where the typical ash content varies between 30-35%; makes coal cleaning operation necessary before its utilization. Prior to coal cleaning operation, coal is grounded to -13 mm and is separated to coarse fraction (-13 mm+0.5 mm) and fine fraction (-0.5 mm). Fine fraction of coal is washed through froth floatation process, which generates tailings coal as by-product. Tailings coal is a high ash reject fraction with ash content ranging 30-40% depending on feed coal ash content and process conditions of froth flotation process.
[003] Rejects of froth flotation process, is a fine sized coal cake with surface moisture that varies between 25-30%, part of which is presently used for foundry applications. Storage of the tailings coal is an environment concern, since it is a fine fraction and is stored in slurry condition. Further beneficiation of this material at same particle size of -0.5 mm by using other physical beneficiation methods is difficult, as the ash is finely distributed. Hence, process is established for segregation of the low ash coal by centrifugation at ultrafine size. As the ash particles are heterogeneously distributed inside coal macerals, further cleaning of tailings coal directly, is difficult. In this present disclosure, a two-stage methodology is proposed for generating the clean coal from tailings coal.

Summary of Invention
[004] Before the present systems and methods for an adjustable ship shore support bracket, are described, it is to be understood that this application is not limited to the particular systems, and methodologies described, as there can be multiple possible embodiments which are not expressly illustrated in the present disclosure. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only and is not intended to limit the scope of the present application. This summary is provided to introduce concepts related to an adjustable ship shore support bracket. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
[005] Accordingly the present disclosure discloses a system for segregation of low ash clean coal from coal tailings comprising at least one crushing mill or crusher configured for grinding coal tailing; at least water source to feed water at various stages of the process of segregation of low ash clean coal from coal tailings; and at least one centrifuge configured to be operated at different speeds for separation of different types of coal.
[006] The process of separation of low ash clean coal from coal tailings comprising the steps of:
• feeding of tailing coal in the crushing mill or crusher along with water for fine and homogenous grinding of coal tailing to a particle size of less than 45 microns and to produce feed coal slurry with a pulp density of 1:1 ratio;
• mixing water in the coal slurry to maintain required coal to water ratio before feeding it to centrifuge to improve particle-particle interaction for good separation;
• feeding the water and coal slurry mixture in a high-speed centrifuge operated at differential speeds for separation of the water and coal slurry mixture into different layers of high ash coal layer, low ash coal layer and water to get an average coal ash of 14.8-16.4% with 58.5-68.9% yield for a feed coal ash of 34.9%;
• removing layer of low ash coal from the centrifuge by scrapping out and discharging it at a predetermined level; and
• removing layer of high ash coal from the centrifuge by scrapping it from the walls of the centrifuge for its separation.

Brief description of accompanying drawing
[007] The foregoing summary, as well as the following detailed description of embodiments, is better understood when read in conjunction with the appended drawing. For the purpose of illustrating the disclosure, there is shown in the present document example constructions of the disclosure, however, the disclosure is not limited to the specific methods and apparatus disclosed in the document and the drawing.
[008] The detailed description is described with reference to the accompanying figure. In the figure, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawing to refer like features and components.
[009] Figure 1 shows the present unit operations at coal preparation plant.
[0010] Figure 2 shows the process flow sheet of the proposed methodology for obtaining clean coal from tailings coal.
[0011] Figure 3 shows the schematic representation of the centrifuge for obtaining clean coal from tailings coal.

Detailed Description of the Invention
[0012] Some embodiments of the present disclosure, illustrating all its features, will now be discussed in detail. The words “obtaining”, “identifying”, “determining”, “calculating”, “computing”, and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms "a", "an" and "the" include plural references unless the context clearly dictates otherwise. Although any systems and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the exemplary, a milling cut collector is now described. The disclosed embodiments of the milling cut collector are merely exemplary of the disclosure, which may be embodied in various forms.
[0013] Various modifications to the embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art will readily recognize that the present disclosure for separation of low ash coal from tailings coal is not intended to be limited to the embodiments illustrated but is to be accorded the widest scope consistent with the principles and features described herein.
[0014] Normally, the Indian run-of-mine coals are with high ash content, where ash is distributed finely in vertical and horizontal directions. As iron and steel making processes require low ash clean coal for coke making, several physical beneficiation stages adopted to enrich low ash clean coal from run of mine coal.
[0015] In a coal preparation plant, coal is preliminarily ground to improve the liberation of ash bearing mineral particles, where fine coals are generated due to over grinding. After the grinding operation, fines are separated by the de-sliming operation and is fed to froth flotation process due to hydrophobic and hydrophilic properties of macerals and minerals respectively. During this process, high ash rejects called flotation tailings are generated as by-products. Flotation tailings are fine sized coal with 0.5 mm as upper limit and ash content varies from 30%-40%. All the different properties of tailings coal are listed in Table-1 and size distribution is listed in Table 2. Currently the application of tailings coal is for foundry purpose; however minor part of the entire pond is used and hence value addition helps in improvement of process economics and makes it more environment friendly.

Table 1: Feed coal properties
Property Concentration, wt. %
Proximate Analysis Inherent moisture 1.63
Volatile matter 21.5
Ash content 34.9
Fixed carbon 42.3
Ash Constituents
Analysis SiO2 20.320
Al2O3 8.010
Fe (T) 2.540
CaO 0.723
MgO 0.252
MnO 0.029
TiO2 0.740
Ultimate Analysis Carbon 80.7
Hydrogen 5.1
Nitrogen 1.3
Sulphur 1.1
Oxygen 11.8
Calorific Value 21.56 MJ/kg

Table 2: Size distribution of tailings (feed) coal
Under pass, % D10 D20 D30 D40 D50 D60 D70 D80 D90 D100
Avg. particle size, micron 48.3 108.5 173.2 233.3 287.0 339.8 404.2 500.1 654.4 660.2

[0016] Beneficiation of tailings coal at the same size using other unit operations will not result in clean coal with significant yield due to limited liberation. Therefore, further size reduction is required. Ultrafine grinding operation thus employed using table top planetary ball mill. Planetary ball mill of 300 ml capacity is used for ultrafine grinding of coal. As tailings coal is in wet form, grinding operation is performed in wet condition. As, the homogenous particle size distribution needs proper movement of balls in the mill, extra water is added to improve flow-ability. Optimized grinding conditions are tabulated in Table 3 and product particle size distribution listed in Table 4. Coal is very finely grinded to a particle size of <45 microns, which makes it difficult to settle. Settling velocity of the coal/mineral particles reduces drastically with reducing the size. Coal slurry with a maximum particle size of 43.7 micron is obtained with grinding at 350 rpm for 30 minutes and 1:1 pulp density. As the settling speed is very low, external push need to be given for the particles.

Table 3: optimum process parameters for ultrafine grinding of feed
Parameter Minimum Increment Maximum Optimum
Grinding speed 250 rpm 50 rpm 350 rpm 350 rpm
Grinding time 15 min 15 min 60 min 30 min
% water addition 70:30 10% 30:70 50:50
Ball size 1 mm 1 mm 4 mm 2 mm

Table 4: Size distribution of ultrafine grinded feed coal
Under pass, % D10 D20 D30 D40 D50 D60 D70 D80 D90 D100
Avg. particle size, micron 2.7 3.8 5.0 6.3 7.7 9.3 11.6 14.8 20.5 43.7

[0017] Next stage of operation is to segregate the low ash coal and hence, different physical cleaning methodologies are tested. As ultrafine coal-water slurry is a homogenous mixture with ultrafine particles, settling time is very high for ash particles and hence separation by sink and float is not feasible. Centrifugation process employed to impart centrifugal force to separate the fine sized clean coal. Centrifugal force is the external force that is applied on the coal /mineral particles to move based on the specific gravity. Centrifugal separation is carried out to separate the low ash clean coal from high ash coal based on the difference in the centrifugal force. High ash coals move fast and settle on the centrifuge surface compared to low ash clean coal. As specific gravity of the water (1.0) is similar to that of clean coal (1.1-1.3), some of the water resides with the clean coal and hence the layer looks to be softer. During centrifugation, based on the properties, three different layers are formed. Third layer is high ash coal, which formed on the surface of the centrifuge walls and is formed due to high density. Second layer is a soft clean coal layer, which forms adjacent to the high ash layer. And the first layer is the water and is formed in the centre of the centrifuge.
[0018] Centrifugation is carried out at different speeds to check the separation efficiency. Optimization of the centrifuge speed is done by operating the centrifuge at different speeds and the objective function is to get low ash clean coal product. It was observed that, increasing centrifuge speed from 2,000 rpm -10,000 rpm improves the separation efficiency and above which, the product quality deteriorates due to the reason that, at high centrifuge speed, the separation between low ash coal and water is much effective, which intern reduces the separation efficiency of the high ash layer and low ash layer. As water is free flowing, it comes out directly. Second layer, which is of low ash coal layer is scrapped out at a particular level and is discharged. Third layer, which is high ash coal layer is scrapped from the walls.
[0019] Case-1: ultrafine grinded coal slurry (for feed as mentioned in table 1) with 1:1 pulp density centrifuged at 3 minutes spinning at 10,000 rpm speed is found as optimum to achieve minimum ash content coal with higher yields. Tests repeated for reproducibility and results are tabulated in Table 5. It was observed that, average ash content obtained at 19.4% with an average yield of 59.2%.

Table 5: Properties of product coal obtained by centrifugation of ultrafine grounded coal
S. No. Clean coal yield, % Clean coal ash, % Rejects yield, % Carbon recovery, %
01 39.13 21.21 60.87 47.36
02 50.44 19.45 49.56 62.41
03 47.99 19.40 52.01 59.42

[0020] Case-2: In order to further lower down the ash and finer separation of coal, interaction of coal particles in the centrifuge is to be improved and hence excess water is added. Centrifugation tests were performed with excess water addition at 1:1 ratio. At optimum water addition, it was observed that, 10000 rpm rate and 3 minutes of centrifugation will be able to yield high amount of product. The final properties of the product are tabulated in Table 6. Ash content of the product varied from 14.8% to 16.4% with a yield ranging from 58.5 to 68.9% for a feed coal ash of 34.9%. Total carbon recovery of 84.5% achieved in clean coal, which can be used for coke making application. Product properties include 43.8% moisture, specific gravity of 1.28 and calorific value of 24.4 MJ/kg (Table 7). Advantages of utilization of this product include not only reduction in process economics and environment related issues, but also improvement in coal mine sustainability. As the study requires a manual separation, an error of +5% in ash and yield is observed and this is assumed due to the loss of some of the high ash reject material inside the centrifuge, loss of nano-sized coal with water layer and coagulation of ultrafine sized coal while drying. However, if future one can do further studies to automate the process, which in turn may reduce the error. It was also observed that, increase in 5% feed coal ash increase the product ash by approximately 2%.

Table 6: Properties of clean coal obtained by centrifugation of ultrafine grounded coal in presence of excess water (for feed as mentioned in table 1)

S. No. Clean coal yield, % Clean coal ash, % Rejects yield, % Carbon recovery, %
1 63.37 14.82 36.63 82.92
2 65.86 16.46 34.14 84.52
3 58.52 15.93 41.48 75.57

Table 7: Properties of low ash clean coal product
Property Value
Moisture 43.81-47.2%
Specific gravity 1.28
Calorific Value 21.9-24.4 MJ/kg (solid powder)

Method of Separation of clean coal from floatation tailings:
[0021] Process for separation of clean coal from floatation tailings consists of a two-stage methodology and is depicted in Figure 2. Initially tailings coal is grounded in a ball mill or more specifically in a planetary ball mill or other grinding device, prior to which water is added to feed coal slurry in order to maintain required coal to water ratio. Ultrafine sized coal water slurry is then centrifuged in a high-speed centrifuge operated at different speeds, and then three different layers are separated out. Extra water is added before centrifugation to improve particle-particle interaction for good separation. First (top) layer is mainly water along with nano sized carbon particles; second (middle) layer is soft coal slurry at lower ash levels; Third (bottom) layer is a hard coal at higher ash level. The collected middle layer, which is a low ash product, is tested for different properties.
[0022] Accordingly the present disclosure discloses a system for segregation of low ash clean coal from coal tailings comprising at least one crushing mill or crusher configured for grinding coal tailing; at least water source to feed water at various stages of the process of segregation of low ash clean coal from coal tailings; and at least one centrifuge configured to be operated at different speeds for separation of different types of coal.
[0023] The coal tailing is configured to be fed to crushing mill or crusher along with water to form coal slurry for maintaining pre-determined coal to water ratio. The crushing mill or crusher is a planetary ball mill configured for forming ultrafine sized coal water slurry. The coal tailings are configured to be grinded in said crushing mill or crusher to a particle size of <45 microns. The high-speed centrifuge operated at different speeds is configured to separate said ultrafine sized coal water slurry in three different layers viz first (top) layer is mainly water along with nano sized carbon particles; second (middle) layer of low ash coal is soft coal slurry at lower ash levels and third (bottom) layer is a hard coal at higher ash level.
[0024] The second layer of low ash coal is configured to be removed from the centrifuge by scrapping out and discharging it at a predetermined level. The third layer of high ash coal layer is configured to be separated from the centrifuge by scrapping from the walls of the centrifuge for its separation. The centrifugation for separation of low ash coal is configured to be carried out in a speed range of 2,000 rpm -10,000 rpm to improve the separation efficiency. The centrifuge is configured for recovering total carbon of 84.5% in clean coal with 43.8% moisture, specific gravity of 1.28 and calorific value of 24.4 MJ/kg, suitable for coke making application.

[0025] The process of separation of low ash clean coal from coal tailings comprising the steps of:
feeding of tailing coal in the crushing mill or crusher along with water for fine and homogenous grinding of coal tailing to a particle size of <45 microns and to produce feed coal slurry with a pulp density of 1:1 ratio;
mixing water in the coal slurry to maintain required coal to water ratio before feeding it to centrifuge to improve particle-particle interaction for good separation;
feeding the water and coal slurry mixture in a high-speed centrifuge operated at differential speeds for separation of the water and coal slurry mixture into different layers of high ash coal layer, low ash coal layer and water to get an average coal ash of 14.8-16.4% with 58.5-68.9% yield for a feed coal ash of 34.9%;
removing layer of low ash coal from the centrifuge by scrapping out and discharging it at a predetermined level; and
removing layer of high ash coal from the centrifuge by scrapping it from the walls of the centrifuge for its separation.