Coal Mining & Supply Management at Thar Block II: Blending, Sampling and Testing Regime

During current pandemic situation Thar Team is effectively managing all coal mining and power plant operations ensuring essential power fed to the national grid.

Coal Mining and Supply Management at Thar Block II: Blending, Sampling and Testing Regime

By Hafiz Tariq Zaman Khan and Muhammad Usman Zafar

Sindh Engro Coal Mining Company (SECMC) an exemplary public private partnership, successfully operates the first ever open pit coal mine of Pakistan in Thar, Block II.

Exploitation of coal ultimately leads to the generation of 660MW from the power plant which is also operated by Engro Powergen Thar Limited (EPTL). SECMC and EPTL achieved their COD on July 10, 2019 by completing all the test and inspection processes, currently mine is in the phase of advancement towards west wall with coal production of 11,000-12,000 tons/day.

Even in current pandemic situation Thar Team is effectively managing all coal mining and power plant operations ensuring essential power fed to the national grid. The coal supply is the backbone of power generation, it is essential to supply the coal as per the requirement and need of power plant.

Geological nature and inherent quality of coal are the main factors which controls the quality of supplied material. Stratigraphically, coal bearing Bara Formation of Paleocene to Early Eocene age unconformably overlies on the Granitic Basement of Pre-Cambrian age.

Bara Formation consist of coal with interbedded claystone/carbonaceous clay and sandstone. Alluvial Deposit of sub-recent age unconformably overlain by Dune Sand and overlies on Bara Formation. Alluvial Deposit consist of dominantly silty claystone, siltstone and sandstone. Dune Sand of recent age is the topmost unit and mainly consist of Sand with minor silt.

Fig. 01: Showing east-west cross-sectional view of sub surface geology

Groundwater is present in three horizons named as: Dune Sand Aquifer (1st Aquifer), Coal Seam Roof Aquifer (2nd Aquifer) and Coal Seam Floor Aquifer (3rd Aquifer). Coal Seam Roof and Floor Aquifers are confined aquifers and Dune Sand Aquifer are phreatic aquifer.

Due to the presence of aquifers beneath the earth, dewatering becomes a backbone of the project. Till date 27 peripheral dewatering wells and 06 in-pit wells are in operation with additional setup of surface drainage pumping station in mine which have the pumping capacity of 1800-1900 m3/hr. Sand which extracted from 2nd Aquifer has been also used for the maintenance of haul and surrounding roads.

Coal bearing Bara Formation is 60 to 80 m thick. The Coal layers in Bara Formation are divided in different layers based on their thicknesses and elevation. These coal layers are interbedded with claystone/carbonaceous clay.

In addition, sand lenses are also reported in this region. Three different terms are being used to classify the waste and coal in mine, “CL” is used for coal, “Interburden-IB” is used for interbedded claystone/waste which has the thickness of >0.5 m and “parting” is used for those interbedded claystone which has thickness of <0.5 m.

Coal layers in Thar Block II Region start from-62 AMSL till -115 AMSL with interbedded claystone/carbonaceous clay. Average cumulative thickness of coal seam is about 25-30 m. Each coal seam possesses different quality parameters which indicated fluctuation in paleo-environment.

Due to variation in coal quality parameters, coal blending and sampling become a backbone of coal supply operations.

Coal blending helps to utilize the maximum resource from mine with keeping all quality parameters in range. Mine has achieved their design depth and successfully extracted the last coal seam from the designed pit shell and currently in the phase of advancement toward west wall.    

Fig. 02: Showing structural variation of coal seams and other lithologies on
west wall of open pit coal mine

SECMC follow the robust coal blending, sampling and testing regime to produce and supply on-spec coal to power plant. Mine geology also a main factor which is being covered by the coal Mining Team as well.

The journey of black gold (coal) from Mine to Power Plant  goes through by several screening processes such as: coal seam roof and floor demarcation and inspection, in situ sampling of coal seam, blending plants, sampling of coal from stockyard after crushing, proximate/general analysis and certificate issuance.

Fig. 03: Flow chart showing the coal blending, sampling and testing regime

Roof and floor demarcation of coal seam is the first step from which the quality of coal has been controlled, identification and removal of waste material, inspection of over-digs and under-digs are the major functions of roof and floor demarcation process, this practice helps to utilize the maximum resource of coal and minimize the probability of dilution.

Fig. 04: Showing the exposed roof of coal seams after roof cleaning and inspection

In situ sampling helps in the upgradation of Resource model and provide an edge during the planning of daily blends of coal. As Bara Formation consist of different layers of coal which have different quality parameters, so it is necessary to make a blend of coal seams on daily basis to fulfil the requirement of Power plant. Blending plan is developed on the basis of Resource model, in situ sampling analysis, exposure and availability of coal seams.

Fig. 05: Trenching for the collection of fresh in-situ coal sample from open pit coal mine

Coal is extracted from mine by using excavators and transported to crushing plant via dump trucks, crushing plant sizes the coal to <350 mm nominal top size, sampling of crushed coal from stockyard is an integral part of coal crushing. Continuous time-based coal sampling is carried out by using ISO standards such as ISO: 13909-1 and ISO: 18283:2006.  

Coal sampling is a continuous process integrated to Production, all the increments are collected in sample bags which covered by double polythene bags and transported to coal lab at the end of the day or production. One composite sample of whole day production is being prepared and sent to lab for Proximate/General analysis.

Fig. 06: Proximate/General analysis of coal sample in coal testing lab

Prepared air-dried sample(s) sent for proximate/general analysis which include Total Moisture, Ash, Sulphur, Net Calorific value, Volatile Matter and Fixed Carbon. All the proximate/general analysis are carried out using ISO Standards and results are reported on “as received basis”. Third party duly witness all the sampling and testing regime.

Core responsibilities of third party is to witness the whole coal sampling and testing protocols, verify equipment calibration, validity of reagents and generation of report or certificate. After issuance of certificate by third party, certified coal stockpile is ready to supply. On average SECMC supply 12,000 tons/day on-spec certified coal to power plant via dump trucks.

Fig. 07: Issuance and signing of certificate which leads to coal supply
to power plants via dump trucks

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