Thar Coal combustion — A solution to an era of energy crisis: Researcher Asim Rizvi
As the demand for electrical power in this day and age continues to increase with the increase in population and technological and economical advancements, the presence of a stable framework for power generation in Pakistan has become absolutely imperative.
Over the past decade, Pakistan has been undergoing an era of serious energy crisis and the situation has worsened in the past 10 years affecting the industry and our daily lives. This energy crisis is solely due to the fact that power from coal resources in Pakistan has not yet been harnessed efficiently, if at all. However, due to the increased awareness concerning the prevalent energy crisis both in the public sector and especially the industrial sector, in Pakistan, people now feel the need to bring about a considerable change in the prevailing conditions. Hence, with the present government, extensive work is being performed on various forms of renewable energy especially coal-related projects.
Most important for Pakistan’s current energy crisis is the Thar coalfield in Sindh which is the world’s largest lignite coal reserve comprising 175 billion tons spread over 9600 km2, and having an electrical potential equivalent to 100,000 MW. The first indication of the presence of coal in the Thar Desert was reported while drilling water wells by the British Overseas Development Agency (ODA) in coordination with the Sindh Arid Zone Development Authority (SAZDA) in 1992. Due to the lack of intensive investigation, the role of coal
in the energy mix never gained significant importance in Pakistan. However, the coal obtained from the Thar coalfield would enable the mitigation of the present 5000 MW electricity shortfall and would certainly facilitate our country in meeting any electricity demands in the future.
The process for obtaining energy from Thar coal has been subject to a lot of debate with experimentalists stating that gasification is the technique to be used. While that is a useful means of obtaining energy from coal, it is not viable for Thar coal purely based on the geology of the Thar coalfield; the presence of aquifers around the Thar coal seams would lead to groundwater contamination by the gasification process. Therefore, open-pit or drift mining is the more feasible approach in the efficient removal of the Thar coal. Certainly, the mined coal will have to be stored under low temperatures so as to avoid ignition but overall this approach is an easier and more efficient way to mine and then store Thar coal. In conjunction with efficient mining of Thar coal, retrofitting of the present boilers used in oil-based pow
er plants with a tube-based design should also be employed.
Power generation through coal combustion is only one aspect of the grand design as it is also essential to take into consideration the environmental hazards of irresponsibly combusting coal at an industrial scale. As coal is likely to remain important in the electricity production in Pakistan for quite a number of years, gaseous emissions control will be mandatory and this can be achieved by implementing clean coal technologies; they involve responsibly combusting coal in coal-fired power plants by keeping the gaseous emissions of NOx, CO2 and SOx in the flue (exhaust) gases at a controlled minimum based on environmental regulations. NOx, CO2 and SOx have many harmful effects of which some are airborne diseases, corrosion in boilers and most importantly, the Greenhouse Effect leading to global warming.
The National Oceanic and Atmospheric Administration stated that the Earth’s average temperature in April 2016 was 13.7 oC. This was about 1.1 oC warmer than the Earth’s 20th century average recorded temperature. The hottest regions on the planet were Africa, South America and Asia. Even looking at the current month of May in Pakistan, temperatures have been increasing upto and staying constant in the mid to high 40s. The cause of these high temperatures is due to global warming. Therefore, keeping the high gaseous emissions obtained throu
gh coal combustion to an absolute minimum by using specialized combustion techniques was the basis of my Ph.D. research.
I performed lab-scale kinetic experiments on a suite of Pakistani coals including Thar coal using thermogravimetric analysis and different combustion atmospheres comprising 21% O2-79% N2 (Air), 30% O2-70% N2 (Enriched-Air), 21% O2-79% CO2 (Oxy-fuel) and 30% O2-70% CO2 (Enriched Oxy-fuel) at heating rates of 10 and 40 0C/min so as to understand and hence, compare the effects of the two heating rates and the four oxidants on the thermal degradation of these Pakistani coals particularly their devolatilization (loss in volatiles). The objective was to investigate the reactivity of Thar coal at different heating rates and in different combustion environments. This in-depth data was then processed to find out the activation energies of the Thar coal. The graphs in Figures 1 and 2 are indicati
ve of the fact that Thar coal proved to be most reactive amongst the other coals as it showed a very high rate of mass loss. This work on kinetic analysis of Thar coal has already been published in the American Journal of Energy & Fuels and can be accessed online.
Successful pilot-scale combustion experiments were then carried out on Thar lignite by blending it in ratios of 5%, 10%, 15%, 20% and 25% with a high-grade bituminous coal and combusting these blends in 20 kWth and 50 kWth down-fired furnaces using a specialized oxidant delivery technique known as Air-Staging. Air-staging involves controlling the amount of oxidant in those combustion zones where it is critical for NOx formation, and so NOx reduction can be achieved. It was through using this technique that the gaseous emissions of NOx, CO2 and SOx were controlled to a minimum and I was able to achieve a 76% reduction in NOx levels (Figure 3). This work on pilot-scale combustion of Thar coal has also been published in the American Journal of Energy & Fuels and can be accessed online.
Before we can even contemplate mining the coal and/or erecting power plants, detailed R&D must be carried out which also includes a feasibility study on which coal would be most suitable for power generation at an industrial scale. The kinetic data and combustion data obtained through my Ph.D. research can be used directly by power plant engineers as a selection criteria for Thar coal to be used for power generation and when establishing the optimum combustion configurations for coal-fired power plants.
My Ph.D. research was performed under the regular split Ph.D. program of the University of the Punjab. Therefore, all lab-scale and pilot-scale experimental work on Thar coal was carried out at the University of Leeds (UK), the Low Carbon Combustion Centre (LCCC) in Beighton, Sheffield (UK) and at International Innovative Technologies (IIT) in Gateshead, Newcastle (UK). The plethora of results from my research were processed at the Institute of Chemical Engineering & Technology, University of the Punjab. The Thar coal was provided by Deep Rock Drilling Private, Ltd., Karachi (PAK) to the University of Leeds (UK).
These pilot-scale experimental facilities will also be available in Pakistan in the near future at the Centre for Coal Technology, University of the Punjab due to the efforts of Prof. Dr. Shahid Munir (Director, Centre for Coal Technology). Such research facilities will prove to be an asset to Pakistan in the years to come.
Lastly, the entirety of my research work would not have been possible without the funding (Rs. 42 lakhs) provided by University of the Punjab and our Vice Chancellor Prof. Dr. Mujahid Kamran, whose unwavering support is always present to motivate us all in working towar
ds the prosperity of our country.
The author is currently teaching as an Assistant Professor at the Institute of Chemical Engineering & Technology, University of the Punjab, Lahore ([email protected]).