Environmental Indexing of Sustainable Lignite Deposits at Thar Coal Field

Pakistan’s lignite coal deposit was discovered by Geological Survey of Pakistan in the 1990s and it spreads over more than 9,000 km2 area comprises around 175 billion tons enough to meet the country’s fuel requirements for centuries.

Sustainable Lignite Deposits At Thar Coalfield

By Waqas Abdul Aziz and Ali Iqtidar

Lignite, generally yellow to dark brown or rarely black coal that formed from peat at shallow depths and temperatures lower than 100 °C (212 °F). It is the first product of coalification and is intermediate between peat and subbituminous coal according to the standard coal classification used in the United States and Canada.

It has been estimated that nearly half of the world’s total proven coal reserves are made up of lignite and subbituminous coal, but lignite has not been exploited to any great extent, because it is inferior to higher-rank coals (e.g., bituminous coal) in calorific value, ease of handling, and storage stability.

In areas where other fuels are scarce, the production of brown coal far exceeds that of bituminous coal. Most lignite’s are geologically young, generally having formed during the Mesozoic and Cenozoic geological age (approx. 250 million years ago to the present).

Pakistan has emerged as one of the leading countries of the world after the discovery of huge lignite coal resources in Thar, Sindh. Pakistan has the seventh largest coal deposit in the world amongst the USA, Russia, Australia, Germany, China and Poland.

Pakistan’s lignite coal deposit was discovered by Geological Survey of Pakistan in 1990s and it spreads over more than 9,000 km2 area comprises of around 175 billion tons enough to meet the country’s fuel requirements for centuries. The economic lignite deposit of Pakistan is restricted to Paleocene and Eocene age (approx. 70 million years old) rock sequences.

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(Left) Dump truck transporting coal from mine to stockyard. (Right) Conveyor belt carrying crushed coal for stacking and reclaiming.

Lignite coal mining in Pakistan has always been considered as an environmental threat due to various myths which aren’t based upon any technical rationale. One of the most common myth to halt utilization of Thar coal is that this coal has high sulfur and ash (combusted product of coal) contents.

Sulfur in coal is fundamentally originates from either organic (pollen) or inorganic (pyrite) sources. Sulfur and Ash are the two most globally known potential environmental risk ingredients in coal-fired power plants.

However, as the power generation technology is getting advanced, sulfur and ash production from coal combustion can be effectively controlled and even reduced to the standard acceptable limits making it to an environmentally friendly component.

Thar coal in comparison with international lignite coal

In order to provide with a technical explanation against all the coal quality myths being considered for Thar coal deposit, Environmental Indexing based on the reported concentrations of sulfur and ash parameters have been done for Thar Coal in comparison with globally renowned lignite coal deposits.

Coming down to the facts, the sulfur and ash values for nearly topmost large scale globally recognized lignite coal deposits have been compared with Thar coal and are summarized below. Before proceeding any further, author wish to express that the data accumulation, compilation as well as QA/QC has been done by a competent Team of Resource Geologists with diverse experience and skills.

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From the data collected and shown in graphs, it can be observed that the sulfur and ash concentrations of Thar coal deposit are very less i.e. 1.0% and 7.4% respectively and included among the good quality lignite coals of the world which are well known for their inherent environmentally friendly characteristics.

Further, Thar coal sulfur and ash values are also very identical to the lignite deposits of USA and Russia which are the top 02 lignite producing giants of the world. Moreover, Thar coal also proven to be much better than the lignite deposits of Poland, India, Indonesia and Turkey.

This shall now be concluded with the fact that Thar coal can be effectively utilized to its full capacity as it has very negligible proportion of sulfur and ash which can barely affect local or regional environment. In addition, Spontaneous Combustion and Acid Rock Drainage (ARD) are also treated as major environmental hazards regarding coal mining and power generation.

Both hazards are predominantly triggered by the concentrations of sulfur present in coal. Sindh Engro Coal Mining Company at its Lignite Coal Mine in Thar Coal Block II has placed all potential controls to eliminate these environmental hazards associated with coal mining.

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Spontaneous combustion of coal is the process of self-heating resulting eventually in its ignition caused by the oxidation of coal (primarily sulfur bearing pyritic coal) when it is exposed to the atmosphere. It usually occurs at coal stockyards where coal is being storage for longer time periods.

Spontaneous combustion at Thar coal mine is being controlled by reducing the coal storage time at coal stockyard and by limiting the exposure of coal seams at mining pit to a minimum possible. Acid Rock Drainage (ARD) also known as Acid Mine Drainage (AMD) describes the formation of acid when sulfide bearing mine wastes (principally pyrite) are exposed to oxidizing conditions, typically in the presence of water, due to groundwater, rain and run-off. 

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Dumping area has the highest potential risk of acid rock drainage where acid prone material is being dumped and exposed to sunlight for oxidation which can result in acid generation and drainage to underground.

However, Storage areas like coal stockyard, ROM pad etc. has very least ARD risk since coal or pyrite bearing wastes are being stored at such areas for lesser time period thus eliminating the process of oxidization.

Likewise, Spontaneous Combustion, Acid Rock Drainage is also being effectively controlled during mining operations at Thar coal mine by dumping the Potential Acid Forming (PAF) rocks sequentially with Acid Neutralizing Material (Dune Sand) in the form of alternate layers and sealing both the materials completely with the non-permeable clay from bottom, top and sides to eliminate seepage.

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Thar Coal Mine Dumping area showing sequential dumping of Acid Prone Material with Acid Neutralizing Material and sealing them from all sides with Clay

Apart from this, another major environmental concern associated with the combustion of coal is the emission of toxic contaminants such as Sulfur Oxides (SOx) and Nitrogen Oxides (NOx) which affects human and environmental health.

Engro Powergen Thar Limited is running 2 * 330 MW coal fired power plant at Thar Coal Block II from indigenous Thar lignite coal has equipped with advanced technology based Circulating Fluidized Bed (CFB) boiler which is rated as an environmentally friendly boiler for power generation.

CFB doesn’t require any back-end equipment for sulfur and nitrogen emission controls. It uses limestone as a catalyst which controls the release of SOx and NOx during coal combustion to a minimum and within the specified NEQS/IFC guidelines.

Various national and international auditors have also acknowledged the fact that coal production and power generation at Thar Coal Block II is being done in accordance with standard HSE guidelines and has adapted the best practices for environmental compliance.

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