Keywords

1 Introduction

Energy demand is a major step of the growing population. Many researchers are trying to find out the alternative forms of energy. There are different ways of alternative energy sources, but Indian waste coal has the unique advantage as an energy source. Large amount of waste coal is reserved underground in Indian coal mines, especially in west zone coalmines. Indian waste coal cannot be conveniently used like fine coal because Indian waste coal has low caloric value and high moisture content. Therefore, the utilization of waste coal is far from satisfying in the world (Tanigaki et al. 2012; Liu et al. 2016; Belgiorno et al. 2003). Many methods have been developed in order to use Indian waste coal as an energy source since the 1920s. There are some technical steps for utilization of low-rank coal-like steam drying, supercritical water drying and hydro-thermal–mechanical compression drying (Koukouzas et al. 2008; Morris and Waldheim 1998). The future energy resources and chemicals supply basically depends on efficient and cost-effective utilization of Indian waste coal. In case of energy source, Indian waste coal is well known because it has high concentration of oxygen-containing functional groups and high proportion of transitional (Pan et al. 2000). Gasification is the process in which any carbonaceous fuel can be converted into a gaseous product and it will be used for energy conversion (Shehzad et al. 2016). Gasification of Indian waste coal as an energy resource is a current domain in all over the world. There are many thermo-chemical conversion methods for conversion of coal into fuel such as pyrolysis can justify the weight loss profile with respect to time and temperature from a variety of sources including waste category coal into liquid, solid and gaseous fuels (Idris et al. 2010; Mondal et al. 2018; Saini and Srivastava 2017).

In the present study, a literature survey has been made to evaluate the status and identify the problems on uses of Indian waste coal. The study also aims at encouraging researchers to work towards the improvement of the present overview on Indian waste coal through suggestions and recommendations.

2 Availability of Coal in India

India is the world’s sixth-largest energy market in the world. The quantity of different quality of Indian coals depends on different conditions like standard of living, degree of commercial activities and different geological phenomena. In case of waste category coal washing is an important step for efficient industrial use. The production of waste category coal requires less ash content to minimize the formation of energy consuming. Percentage of moisture present in waste coal can affects the gasification process. In Indian waste coal moisture is between 7 and 13% (Dwivedi et al. 2018). The availability of Indian coal in different state listed in Table 1.

Table 1 State wise distribution of coal resources
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3 Characterization and Composition of Indian Waste Coal

3.1 Proximate and Ultimate Analysis

Chemical properties of Indian waste coal are an essential step to evaluate the alternative processing and recovery options of coal samples. It has two major steps first proximate analysis and second is ultimate analysis. The approximate values for proximate and ultimate analysis for Indian waste coal are described below as follows:

3.1.1 Proximate Analysis

With the help of proximate analysis, we can evaluate the amount of moisture, volatile matter, total ash and fixed carbon in any coal samples as shown in Table 2.

Table 2 Proximate analysis for Indian waste coal
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3.1.2 Ultimate Analysis

Ultimate analysis is the process to calculate the percentage of carbon, hydrogen, oxygen, nitrogen, sulphur and ash in Indian waste coal samples. The approximate values for ultimate analysis for Indian waste coal are shown in Table 3.

Table 3 Ultimate analysis for Indian waste coal
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4 Thermal Treatment Techniques Applied for Utilization of Indian Waste Coal

4.1 Pyrolysis

Pyrolysis is a thermo-chemical conversion of a sample with respect to time and temperature. During the pyrolysis process, no flue gas is required to utilization. Basically, pyrolysis is a thermo-chemical conversion process that helps to evaluate the physio-chemical properties of samples (coal, biomass, etc.) with respect to time and temperature (Dwivedi et al. 2018). The pyrolysis study of coal mostly shows the thermo-chemical conversion of material with defined time and temperature conditions. The hole process includes different chemical reactions in mainly in three stages with releases of volatile matter second is fast pyrolysis and third is slow pyrolysis process. In the first stage about 70% weight losses in case of waste coal. So the pyrolysis of Indian coal helps to examine the ignition, rate of combustion and particle emission of coal. In the other hand, we can say that it is a method char production to improve its calorific value. During the gasification and co-combustion process, thermo-chemical conversion of coal plays an important role and also helpful for the design and development of boiler and gasifier. Coal pyrolysis passes mainly in two steps first is de-polymerization where vapour, gas and tar are formed and second is re-polymerization where char forming occurs. Mass loss of coal can be measured by using pyrolysis. During the thermo-gravimetric analysis of coal in terms of coal pyrolysis we can calculate weight loss percentage and maximum weight loss at peak of temperature with the help of TG and DTG profiles. The kinetic parameters such as activation energy and pre-exponential factors can be calculated through model-free analysis which may be useful in terms of development of pyrolysis technology and design of reactors (Table 4).

Table 4 Literature survey for TGA with operating conditions and status
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4.2 Gasification Technologies for Indian Waste Coal

Coal gasification technology is one of the most common technologies in India. Different types of solid waste like plastic waste and waste coal are dried and granulated to obtain required particle size for gasification at 700–900 °C. After discharging of gas and char, it may be utilized via combustion in a boiler to raise steam. Gasification can convert carbonaceous fuel into gaseous products.

Gasification of Indian waste coal as an energy recovery process and nowadays it is a current research domain in all over the world. Several researches focused on municipal solid waste gasification technologies by using fluidized-bed system. The fluidized-bed reactor technology has key role in the gasification of solid waste like coal and biomass (Idris et al. 2010; Mondal et al. 2018; Saini and Srivastava 2017). The syngas production and gas-heating value can be helpful to justify the feasibility of fluidized-bed system. Figure 1 shows the common thermo-chemical process and their output for utilization of waste coal (Fig. 2).

Fig. 1
figure 1

Consumption of waste coal in India

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Fig. 2
figure 2

Thermo-chemical process and their output for utilization of Indian waste coal

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5 Some Treatment Strategies to Reduce Environmental Impacts of Indian Waste Coal

Indian coal generally has more ash content and low calorific value, which makes it undesirable for industrial purpose. Indian waste category coal needs washing to make it suitable because it has more ash content. Normal Indian coal generally is more suitable because it has less ash content but it has some another harmfully materials which can reduce gasification efficiency. Since, in India coal mining, regarding uses of waste coal has many issues so it is necessary to manage with good impact its utilization (Pan et al. 2000; Shehzad et al. 2016; Idris et al. 2010). Earlier research also developed some mineral matter and sulphur exhibit harmful effects on utilization of Indian waste coal. So removing of sulphur and high ash content is essential for utilization of waste coal used in different industries (Mondal et al. 2018). Many other ways is on the way to promote the uses of Indian waste coal samples such as some gasification technology-based fluidized-bed gasifier systems (Saini and Srivastava 2017).

6 Conclusion

Continuously improvement on waste management systems is an ever on-going process. In this review article, it is justified that we can use Indian waste coal in the form of pyrolysis and gasification. It is concluded that Indian waste coal utilization can be considered as future energy source with caution. Finally, the study concluded that with some new technologies and with some thermal treatment Indian waste coal can be used as an energy source. The various technologies of gasification and pyrolysis presented in this paper and have contributed greatly to the eco-image of waste management and particularly to Indian waste category uses, treatment and recovery. Using of waste category coal will certainly benefit the current situation. It is very important to consider recycling and energy recovery methods for utilization of Indian waste coal. This study required many further research and development in near future.