KARACHI, Dec 9: The Thar coal is suitable as a solid fuel in its natural form, needs less amount of energy to start ignition for burning process and its combustion is also safe for environment as it produces less ash and poisonous gases, a recently published study says.

The research titled Kinetic studies of pyrolysis and combustion of Thar coal by thermogravimetry and chemometric data analysis has been published in the Journal of Thermal Analysis and Calorimetry.

Anila Sarwar, a PhD scholar of the Fuel Research Centre, Pakistan Council of Scientific and Industrial Research, has conducted the research under the supervision of Prof Dr Mohammad Nasiruddin Khan of Karachi University’s chemistry department.

The study focuses on the quality and reactivity assessment of the newly developed block five of the Thar coal. The primary objective of the effort was to access the quality of the coal and set up a database for the reactivity measurement in order to understand the suitability of the coal for design and scale up of commercial plants.

The most important finding of the study is the ranking of coal as lignite to sub-bituminous (a type of coal primarily used as fuel for steam-electric power generation) using standard classification of coal by American Standard and Testing Materials (ASTM).

“The samples were characterised as high moisture, high volatile matter and low ash. High moisture (i.e. between 21 and 44 per cent) lowers the flame temperature and increases transportation cost. High volatile (more than 29pc) is good for the stability of flame and it suggests that the coal is suitable for combustion and gasification purposes. Hence, it may be used as a solid fuel for combustion in boiler or it may be converted easily into gaseous products,” the study says.

Most samples, according to the study, were characterised as low ash (less than 10 per cent) and low sulfur (less than 2pc).

Therefore, the combustion of coal is considered safe for environmental concern as it produces little ash and low amount of SOx (oxides of sulfur) gases.

“Ignition temperature (the temperature required to start ignition) of the coal varied from 315°C to 450°C. The activation energy (Ea) for pyrolysis and combustion reactions was calculated as 35.50 and 34.27 kJ/mol, respectively.

“It is significantly less than the Ea of other foreign coals. Low activation energy values of Thar coal categorise it as a reactive coal and can undergo pyrolysis and combustion reactions easily,” the paper says.

“On the basis of the characterisation and reactivity measurements, it has been concluded that the coal is suitable as a solid fuel in its natural form especially in power plants and in the designing of industrial coal-fired boiler furnaces,” says Dr Nasiruddin Khan.

He adds that low sulfur content and ash in Thar coal ranks it at a better position from other coals as it will help reduce repair and maintenance cost significantly.

“Reduction in repair and maintenance cost of the coal-based power generation plant is an attractive economical aspect of Thar coal. The study also showed that the coal has the potential to convert into gaseous products and liquid fuel easily with a good yield of products which may act as a substitute for oil or natural gas,” he explains.

Highlighting the significance of the research, the professor says that the Thar coal is better in quality than the Lakhra coal that is characterised as low quality coal as it has high amount of sulfur content (between 1.2 and 14.8 per cent), and high ash (between 4.3 and 49). “High ash and high sulfur content in coal damages plant, which then requires regular maintenance,” he says.

Explaining the reasons for Lakhra power plant’s failure, he says that three units of 50MW each of the Lakhra plant (based on Lakhra coalfield in Dadu district) had been constructed by a China-based company in 1995.

The Chinese, Dr Khan says, had submitted some recommendations at the time of handing over the power plant to the authorities concerned. One of these recommendations was that all the three units should go through comprehensive service every four to five years, he says.

“The company had also recommended that each plant should operate for three weeks and remain closed for maintenance in the last week. Unfortunately, these suggestions have not been followed,” he adds.

According to Dr Khan, all the units of the only coal-fired power plant of Pakistan have not been operational since 2006 because of some leasing dispute between the Jamshoro Joint Venture and Water and Power Development Authority as no funds could be released for regular maintenance and rehabilitation of the plant.

The Thar coal, he says, was discovered in 1991 and the Geological Survey of Pakistan developed four blocks between 1994 and 2000. Yet no comprehensive study was conducted on the characterisation of the coal before this research work, while there was little data in which the coal was ranked as low quality lignite.

In the light of the previous coal-based power plant experience, there is a strong need to learn from the past mistakes and explore new reserves that have the potential to be used as raw material, he says, adding that the characterisation and combustion study of the newly explored reserve is the first step towards its proper utilisation.



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