Recent Advancements in BATAC® Jigging Technology
Gurudas Mustafi (1) and Sushil Kr Dubey (2)
(1) Wholetime Director & CEO, MBE - CMT India Private Limited, Ecospace, Kolkata- 700156, India, email: gm@mbecl.co.in (corresponding author)
(2) Senior Process Engineer, MBE - CMT India Private Limited, Ecospace, Kolkata- 700156, India email: sushil.dubey@mbecl.co.in
Abstract: -
The demand for Low ash coal has increased drastically in the last few years and is likely to remain on a stable high production level for years to come. With the decline of existing and known low ash coal resources, the coal industry will be forced to implement more and more advanced beneficiation techniques.
Jigging is one of the most widely used methodologies for upgradation of coal. The jigging technology has undergone immense modification from manually operated to fully automatic technology over the years. The focused areas such as control of pulsation cycle, effective utilization of jigging area to maximize capacity, control automation, advanced feed and discharge assemblies etc. have resulted in efficient and more accurate jigging.
This paper describes the improvement/modifications done in BATAC® jigging technology and its effect on the performance of the equipment, performance of the coal washeries were also discussed where these modifications have been carried out.
Key Words: - Washeries, BATAC®, Technological Upgrades, Efficiency, Recent Advancement
Introduction
Jig is most widely used coal cleaning technology and is preferred over more expensive dense media circuit, where the “near gravity” material is least. The coking coal reserves of India are not impressive hence it has to import huge quantity of hard coking coal from other countries. Regarding non-coking coal India has good reserve of non-coking coal in the world but it is ironic that we import a huge quantity of non-coking coal too from other countries. The basic reasons for this perplexing reality may be several, which includes costs, quality, availability etc. The major use of non-coking coal is in thermal power plant. As with each passing day the demand for power in India is increasing and in order to make electricity available to every citizen, supply of non-coking coal has to increase. This fact has been realized in many forums, that India should become self- dependent for non- coking coal which will help it save billions of dollars of foreign exchange and also enable it reduce its current account deficit (CAD).
Beneficiation of coking coal/non-coking coal is done based upon the specific gravity of the solid particles. To achieve the above objective BATAC® jig plays the major role, the coarse size range when washed it form a separation bed based on the specific gravity and size. Through consolidation and trickling fine grain will not settle as rapidly as larger particle under the influence of gravity. Thus after one pulsation and suction cycle the grain will be dilated and fines grains will be on the top while coarse and high specific gravity grain will be at the bottom of the bed.
The new BATAC® Jig with under bed pulsation with high throughput rate:-
Lump Ore
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75-90 tph/m width
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Fine Ore
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68-78 tph/m width
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Coarse Coal
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90-110 tph/m width
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Middle Coal
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75-95 tph/m width
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Fine Coal
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65-85 tph/m width
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In the new BATAC® Jig air from the compressor is electronically control through flap valve system (Fig. 2) (pulse generator) and is discharged in air chambers underneath the jig bed instead of adjacent to the screen plate. More over the make-up water is added at the lowest location of every jigging chamber to intensify the upward current and to dampen the downward current. In order to maintain an accurate cut-point of the jigging process, the thickness of the material layers is sensed continuously using ultrasonic (Fig. 3) displacement measuring systems; their measuring values represent the input for PID (Fig. 4) controllers from which the hydraulic systems of the discharge gates are actuated.
Comparative Study of Characteristics of the old and new BATAC® Jig system
The basic fundamental (Stratification, pulsation, suction) of jigging remained the same in both the older jigs and the new jigs. However, the ways in which these principles were affected were changed over the due course of time with better mechanical design and better controls. Above all to be more cost economic more controlled operation is essential for example in Old System bed depth and discharge gates are controlled using Linear Variable Differential Transformer (LVDT) which was based on the principle of conversion of mechanical displacement into electrical signals, these conversion are not so effective which will lead to operator to take corrective action from time to time. This was efficiently improved using Ultrasonic sensors, which is more sensitive and requires less maintenance.
Following table compares the most significant differences between the old and the new system.
Table 1: Comparison between Old and New BATAC® Jig System
Sl. No.
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Old System
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New System
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1
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Card based control panel was used in the older BATAC® jigs which consisted of protonic controller and relay logic, hence interlocking was only possible through hardware changes
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New PLC based control panel has been incorporated which made the control system more efficient and less cumbersome and any changes in logic could be made through simple changes in the software only and no hardware changes were required
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2
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Number of bed height measurement mechanisms (scanning device) and discharge gates across the width of old BATAC® jigs were fewer, at a minimum width of 2m
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Number of bed height measurement mechanisms (scanning device) and discharge gates across the width of the new system for BATAC® jigs were increased, at a minimum width of 1.5m
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3
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Measurement of bed depth and discharge gates’ level were done by Linear Variable Differential Transformer (LVDT) which was based on the principle of conversion of mechanical displacement into electrical signals
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Measurement of bed depth and discharge gates’ level in the new system is being done by using new improved Ultrasonic sensors, which is more sensitive and require less maintenance
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4
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Level of discharge gates was controlled by a centralized hydraulic system which meant that the level of discharge gates at all times remained similar to each other
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Each discharge gate is supplied with an independent control and dedicated hydraulic system which meant that gates could operate independent of each other and is only dependent on the feedback of its associated scanning device and control panel logic
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5
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Working air control unit was of Askania type
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Electronically controlled air control unit is used which can be set individually by means of decade switches. The specific pulsation of every chamber is generated using additional time cards
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6
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Air bypass system of the air control unit, which is the heart of BATAC® jig, was carried out through motorized valves
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Air bypass system of the air control unit were carried out through electro- pneumatic valves which is more sensitive and has less response time
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7
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Hutch section of the old BATAC® jigs consisted of Boat and H section
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New improved hutch section design were provided which replaced the old Boat and H section which made pulsations more smooth and is maintenance friendly
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8
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Local push button station (LPBS) was not provided for the discharge gates
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New LPBS were provided at each discharge gate for ease of doing maintenance
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The original mechanical design of BATAC® is still relevant in today’s mineral processing industry and works with superior efficiency. Major modification is carried out in controls; instrumentation and logic to suit the present coal characteristics and product quality requirements.
Advantages of the new system
The most important and also the most visible advantage of new BATAC® jigs are as follows:
(1) As the control panel was PLC based, changes in logic could be made very easily by just changing the software program. No hardware links were required in order to change the logic as were required in the old system. This made the control system less cumbersome and more resilient. It could now be easily adapted with the changing raw coal feed characteristics.
(2) The PLC system reduced the amount of control wires requirement by about 25% which proved to be very economic.
(3) Increase in number of discharge gates made the discharge system more sensitive.
(4) As the discharge gates were now made independent of each other, the quality control became more efficient. The activity of the gate is now solely controlled by the depth of bed which the floats measured and not dependent on how the other gates were acting. This reduced the misplacement of cleans into rejects.
(5) Pneumatic air flaps used are more efficient and it also reduces the number of motors required. Also options were provided in order to operate the pneumatic valves in manual mode, which enabled the maintenance of such valves in online condition without stopping the whole jig.
(6) Ultrasonic level sensors used are more accurate and sensitive. Hence they helped in adequate quality control and proper working of the discharge gates reducing misplacement.
Advantages of the new discharge devices
The heavy sinks and middling products are discharged into bucket elevators or equivalent discharge
devices via the jig discharge gates and the chamber bottom outlets. The new design of all these discharge devices focuses on aspects of wear and therefore all outlets are built with replaceable, stainless steel insert boxes. Which have following benefits:-
(1) Extended lifetime thanks to the use of stainless steel
(2) No wear occurring at the jig walls proper,
(3) Reduced machining of mechanical components,
(4) Lubrication of bearings is not necessary because of the absence of a shaft,
(5) Rapid replacement of gates and /or insert box.
Conclusion
Considering the fact that the Indian coal has its origin based on the drift occurrence washability of Indian coal is difficult. Thus continuous strengthen of new upgradation is very necessary to economically run the washery. With deteriorating quality of raw coking/non-coking coal poses challenges before the industry to find out simple and economically viable coal washing scheme for maximum recovery of coking/non-coking coal for usage in metallurgical/power sector. Due to these reasons new BATAC® jigs plays a very vital role which is design with more upgraded controls and instruments which will allow to encounter the variation in the raw coal by simple changes in logic of the software only and no hardware changes were required. The new ultrasonic displacement measuring systems not only helps in control discharge but it also control, all jigging parameters (e.g. valve settings, stroke frequency or the working air regulations) can be set directly on site as well as from remote. Thus new process automation has given more space for better controls, leading to absorb the wide range of variation in rom feed.
References
(1) Wills’ Mineral Processing Technology Seventh Edition. (Wills B.A. & Napier T.J.)
(2) Goyal, Piyush, Minister of Power, Government of India- No need to import coal, we have sufficient in India - Financial Express, New Delhi : on 12.06.2017.
