“COMPARISION OFOPERATIONAL DIFFICULTIES IN LONGWALL DIP RISE & STRIKE PANELS” - A.Venkateshwer Reddy, Addl. Manager, Project Planning Department The Singareni Collieries Company Limited
BACK DROP• It is necessity to explore low capacity Longwall mining, where geological conditions permits to work 500m to 1000m length panels in SCCL to get bulk production as well as to reduce the cost of production.
BACK DROP• The major challenges a head is, whether to follow principal stress direction while driving Gate roads or to plan according to the shape of property.• Most of the future Longwall mine panels need to be laid in Dip Rise Direction, if Principal stress direction is taken into consideration.
EXPERIENCE• Though, GDK-10A mine is being worked Strike & Dip rise Panels successfully, the gradient of Dip Rise Panels is 1 in 6 to 7. Where as in the proposed Longwall mines, Dip Rise Panels are around 1 in 4 gradient.
TRUNKS• Formation & Maintenance of Trunk roadways is problem in a direction perpendicular to principal stresses.• Trunk roadways have to maintain longer periods and needs high stability.• Under increased stress condition on gate roads, needs additional supporting like resin bolting, cable bolting, roof stitching, arching etc.
GATE ROADS• More stable when laid parallel to principal stress direction.• Accumulation of Water in dip galleries, increased head of pumping in developing gate roads and insufficient quantity of water for dealing with high head pumps.• Low Gate road progress per month, i.e., less than 100m• If twin or multiple entry system for gate road development adopted in future, drivage is difficult in dip rise panels.• Difficulty in Material Transport and handling on increased gate road gradients.• Necessitates high capacity haulers /conveyor belts, including man riding if provided.
GATE ROADS• Movement of free steered vehicles along gate roads is not feasible on increased gradients.• Only rail car man riding system for men transport along lengthy gate roads is applicable. Chair lift system is not possible as frequent shifting of return pulley while Longwall face under retreat.• Switch train shifting is tedious and generally for every 100 m, necessitates mono rail system for handling cables.• Emulsion supplied to supports could not return to Power pack tank through ring main system, leading poor quality of water emulsion mixture and more consumption of emulsion oil.• Increased Load on relay bars, advancing rams, face sprags of powered roof supports.• Ram capacity & plate size for face sprags of powered roof supports need to be increased.
FACE• Face spalling is more and directly falls between AFC, on spill plates & walkway• Requires advancing chocks by adjacent control due to face spalling while lowering support.• Leading to uneven wear of pans of AFC and flights overriding due to increased cross gradient of face.• Proper cleaning is required for advancing AFC, even shearer provided with cowl.• Shearer goaf side track shoe life reduces as more weight of shearer shifted due to cross gradient factor.• Wear & tear of rack bars & spacers is high, as above.• Less load on shearer haulage due to reduced longitudinal gradient.
FACE• Increased risk to shearer operator &others working nearby due to face spalling.• Subsidence is not uniform due to panel varies from shallow to high depth- possibility of increased breathing from surface.• Whenever heating or fire problem arises, could not easily dealt by method of inertisation and also not possible to drown the workings with water as an ultimate option.• For outby transport of coal in gate road need to provide two or more gate belt drive heads due to increased lift.
FACE• Shearer sump low due to increased cross face gradient.• Face and gate roads are dry if drainage planned is towards the goaf.• Less humid and comfortable ventilation conditions.• Crushing of barrier pillar is minimized compared to strike panels.• In AFC, Gravity component is eliminated for coal transport.• AFC motor capacity to be increased as gravity does not support. (Requires high initial torque).• No slushy condition at BSL.
FACE• Face strata control problems are less.• Periodic weighting interval is less• Cavities formation in face is less due to front abutment pressure is less and more load is shifted to goaf side.• Salvaging is safe and easy due to load on PRS is less.• Face progress is less compared to strike panels.• Property loss is more because of shape of property favors strike panels.• Opined to work one dip rise short length panel in steep seam on experimental basis.
SUMMARY• As far as possible, strike panels are more convenient in operational aspect. Gate roads need to be laid oblique to Principal stress direction and increasing support density to counter the strata control problems.• Wherever strike panels are not feasible keeping in view of shape of deposit and principal stress, it is obvious to work dip rise panels by overcoming the operational difficulties.
CONCLUSION• It is suggested to work Strike panels, instead of Dip Rise Panels in view of the difficulties forecasted in dip rise panels with 1 in 4 gradient.
COMPARISON OF DIP-RISE LONGWALL PANELS WITH STRIKE LONGWALL PANELSS.No Parameters Dip Rise Panels Strike Panels1 Drivage of Single or Moderate Difficult ✕ Easy ✔ multiple Gate roads2 Gate road progress Less ✕ More ✔3 Gate road condition Dry ✔ Slushy ✕4 Material and men Risky ✕ Less Risky ✔ Transport in Gate roads5 Laying & Dismantling Difficult ✕ Easy ✔ of gate belts6 Number of Belts Two or More depends upon ✕ Single ✔ required in Main lift gate7 Switch train Shifting Tedious & cables handling ✕ Easy & shifting can be done ✔ is difficult daily Requires one time shifting for every 100m or more
8 Water Drainage Requires pumping ✕ Does not require pumping ✔ During Development Good ✔ Not Good ✕ During extraction9 Ventilation Comfortable due to dry ✔ Less Comfortable due to ✕ condition humid condition10 Face Spalling More ✕ Less ✔11 Main Weighting Span Less ✔ More ✕12 Periodic weighting Similar ✔ Similar ✔ interval13 Periodic weighting Less ✔ More ✕ intensity14 Strata Control Problems Less ✔ Moderate ✕15 Emulsion requirement More ✕ Less ✔ for supports16 Safety to workmen Less ✕ Moderate ✔17 Load on Shearer Less ✔ More ✕ haulage18 Wear & tear of face More ✕ Less ✔ equipment (AFC & Shearer Parts)19 Face Equipment Creep Less ✔ More & Difficult ✕ problem & Control
20 Sequence of Cutting Limited to Uni-directional ✕ Uni or Bi-directional ✔ only21 Sump to each Cut Less ✕ More ✔22 Production Less ✕ Moderate ✔23 Coal Transport in AFC Gravity does not support ✕ Gravity supports ✔24 AFC Motor Starting High ✕ Moderate ✔ Torque Requirement25 Salvaging & installation Easy ✔ Moderate Difficult ✕26 Dealing of Heating or Difficult & Unsafe ✕ Moderate Difficult & safe ✔ fire Problem27 Subsidence over goaf Non-uniform ✕ More or less Uniform ✔28 Effect of Principal stress More because aligned ✕ Less because aligned parallel ✔ on Trunks perpendicular29 Effect of Principal stress Less because aligned ✔ More because aligned ✕ on gate roads parallel perpendicular30 Alternative to lower Trunks need to be aligned ✔ Gate roads need to aligned ✔ effect of Principal stress oblique to stress direction oblique to stress direction 11 1 19 9 1 1