MINING OF THICK COAL SEAM COAL MINING METHOD BY DC RATKURIA

INTRODUCTION ABOUT THICK COAL SEAM In India seams more than 4.8m thick are considered as thick seam In the former USSR, Poland seams are more than 3.5m thick are known as thick seam In England seam more than 1.8m thick are categorized as a thick seam In India, over 60% of all reserves are contained in thick seam

PROBLEMS ASSOCIATED WITH THICK SEAM MINING Strata control is difficult Heavy support material are required Inspection of roof is difficult Premature collapse Risk of overriding of coal pillars Air blast occur due to collapse of working More chances of spontaneous heating (lost of coal) Sluggish ventilation due to high working The magnitude of subsidence is high Subsidence control is difficult

METHOD OF MINING THICK COAL SEAM Method of mining thick coal seam Bord and pillar Single lift Conventional bord and pillar Hydraulic mining Multi lift Multi lift with full stowing Multi lift with stowing excepting uppermost slice Long wall Single lift long wall Slice mining Under winning

CONTI…….. Single lift longwall Slice mining Inclined slicing Horizontal slicing Diagonal slicing Transversely inclined Under winning integral Sub level caving Inclined horizontal

CHOICE OF METHOD OF MINING THICK COAL SEAM Single lift mining is generally limited to height of 4.8. Recent development of shield support have enabled working of long wall face up to 5.7m height in one pass In west Germany sub level caving method of mining has been successfully applied for 20 m thick coal seam By slice mining the slice being of such thickness as would permit their easy extraction in one pass The basic method in slice mining are bord and pillar and long wall Bord and pillar method of mining in thick seam by multi slicing has not been successful because of strata control poor Long wall method of mining is best suitable for multi slicing mining

SLICE MINING In thi s method of mining coal seam divided into slices These slices are suitable thickness and working individual mining Slice may be taken in ascending or descending order or in mixed order

ASCENDING V/S DESCENDING SLICING Working of first slice in ascending slicing is like working a seam of average thickness Caving is not possible in this method So last slice may be worked with or with out stowing Roof control becomes difficult Spontaneous heating is more Unproductive work is more due to more supporting activities productivity low due to unproductive work Cost of mining is increased

DESCENDING SLICING In descending slicing, working of first slice is like working a seam of moderate thickness and does not present any special difficulty Than other slice working under goaf area of first working and it will necessitate spreading of a netting or material for making artificial roof Possibility of stowing is rarely practiced in descending slicing In this method work done always on firm floor and hence mechanization at face is easier Necessity of netting so increase the over cost of mining Unproductive work due to netting Reduce the OMS due to extra work

THICKNESS OF SLICE The thickness of slice varies between from 2m to 4m There are two main factor or consideration in fixing the thickness of slice 1.To provide sufficient height for the movement of machine and for man to stand in face (not less than 1.8m) 2.Greater the thickness less development work

DISADVANTAGE OF TOO THICK SLICE Extraction of coal from too thick slice is difficult Roof control is difficult Heavy and long timber is required Caving may present difficulties Stowing practice is difficult

FACTOR AFFECTING THE DIVISION OF A SEAM INTO SLICE Thickness of seam Characteristic of roof and floor Thickness and hardness of dirt bands Gassiness of the seam Spontaneous heating Characteristic of coal Mechanization Support cost Labour cost

MAIN SLICING METHODS 1.Inclined slicing 2.Horizontal slicing 3.Diagonal slicing 4.Transversely inclined slicing

INCLINED SLICE In this method the slices are taken parallel to the roof and floor Working in both ascending and descending order In ascending order working with conjunction of stowing Descending order with or without stowing Both method is used bord and pillar or long wall

HORIZONTAL SLICING It is applicable to more than 15m thick seam It can be applied to both hard and soft coal In this method stability of wall rock is not importance It can be done both ascending or descending order When it will done with ascending order filling of goaf must be done Stowing is done with hydraulic and pneumatic

DIAGONAL SLICING It is suitable for working seam with dip more than 50ᶱ It is best method for moderately thick and do not have rock band The seam is opened by level driven in footwall at 50 meter interval Which is sub divide into sub levels This is ensure to gravity flow of broken coal from diagonal slice

Advantages And Disadvantage Of Diagonal Slicing Adv. Gravity flow of coal and filling material in the production face Relatively low volume of main and subsidiary work Unproductive work is low Disadvantages  Filling is essential  Coal losses are high  Timber consumption is high  Method is complex  Working front is small

TRANSVERSELY INCLINED SLICING This method is similarly to horizontal slicing but slices are inclined at an angle of 30ᶱ At the bottom of each slice a level entry is driven for transport of coal to dumping chute In this method the filling material is filled by another chute Slices are extracted by retracted method of longwall

ADVANTAGE AND DISADVANTAGE OF TRANSVERSELY INCLINED SLICING Adv. Gravity flow of the material Minimum volume of subsidiary development work Disadvantage  Total front of working places is shorter  Setting of timber is difficult  Timber consumption is high  Risks of injuries caused by sliding objects This method of mining is not popular

SUBLEVEL CAVING This method of mining is applicable for thick seam with cave able roof and soft coal In this method mining of coal is done by blasting of solids with long hole blasting techniques

CONTI….. This system consist of following 1.Mining a slice along the roof by normal long wall method with caving first slice 2.Mining of another slice along the floor of seam 3.Taking down the coal parting between the two slice by long hole blasting 4.Loaded the broken coal on conveyor laid along the floor of seam The mining in the lower and upper slice can be mechanized by sheares

SUBLEVEL CAVING BY BLASTING GALLERY METHOD In this method the seam is developed in to panel of 100m X 50m From main heading room are driven to the full width of the panel Coal between the room is blasted down to full thickness of seam Coal is loaded by remote controlled loader (mind in safety ) The life of room should be kept as short as possible

Advantage Of Blasting Gallery Method It makes possible to win narrow panel or larger panel according to seam condition It does not require high skilled worker It require relatively less capital investment over the longwall Thick seam up to 15 m can be extracted in one pass This method is highly flexible

CASE STUDY (A INDIAN MINE ) (RAO AND RAO, 1990) In India GDK No. 10 incline in Godavari Valley Coalfield Seam No.3 Thickness of seam 11m A large panel 1000 X 120 X 150m developed and subdivided into 120 X 150m sub panel By driving a raise leaving a barrier of 15m between the subpanel Incubation period varies from 12 month to 18 month

THE EQUIPMENT IN THE PANEL Jumbo drills : 3 LHD : 3 Wheel breaker : 2 Telemonitoring equipment Air winch for servicing LHDs Electrical Gate end panel 40 ton open circuit hydraulic props Chain conveyor Roadheaders Am kW belt conveyor gearhead

WIDE STALL MINING It is the advanced method used for optimal recovery of minerals.(eg:Coal). The conventional method of splitting and stooking of pillars have been replaced by wide stall method. Comparatively, this method is better than splitting and stooking of pillars.

NECESSARY CONDITIONS OF WIDE STALL METHOD Massive immediate roof is an important requirement. If roof is moderate, reinforcement techniques such as cable bolting and roof stitching are used to avoid local deformations. Pillar strength should be more(can be done by increasing w/h ratio). Wide stall method cannot be maintained under weak/laminated roof strata.

CASE STUDY EAST BHUGGATDIH COLLIERY The first field trial of wide stall method was conducted in EBC, situated in Jharia(Jharkhand). It was a successful attempt. It provided nearly 42% coal from a 17 m thick coal seam. No endangering of the surface and subsurface structures because of appropriate strata control measures.