Indian Coal
- Indian coal is having high ash contents. The ash is finally disseminated through the coal so that cleaning of coal is difficult and costly process.
- Washing of coal to reduce the ash content is necessary to obtain low ash metallurgical coal. The washing creates a large proportion of the middlings which can be used as fuel for thermal power plants. Nearly 95% of the total raw coal supplied to washery can be recovered in the form of middlings.
- Average ash content in Indian coal is as high as 20% and as content of middlings at coal washeries lies between 30 to 40%. As such it is inevitable that plants are designed to burn coal of high as content.
- The high ash content of coal reduces thermal efficiency of the boiler, since loss of heat through unburnt carbon, excessive clinker formation and heat in ash is considerably more. It also increases the problem of hot ash disposal. In brief use of coal with high ash content increases the size of the plant, increases the transportation cost of coal of fuel per unit of heat produced and reduces thermal efficiency.
- It also creates problem in the control of the system due to irregular combustion. However, now- a-days such high ash content coals are used as pulverized coal fuel in modern plant and they are used with more economy and increasing thermal efficiency to 90% and simplified controls can be used by adjusting the position of burners in the boilers. Such modern plants are now used in India also.
Liquid fuels:
- Oil can be used in a boiler furnace to generate steam, as a fuel it has number of advantages over others. But the cost of heat produced is high as compared with coal or gas. In India availability being less and hence it is not possible to supply it for thermal plants as fuel.
- Further, it contains more percentage of hydrogen as compared to coal. The moisture carried by the gas per kg of fuel burnt is considerably more. It gives lower overall combustion efficiency of the plant.
Gaseous fuels:
- Gaseous fuels are either natural gas or manufactured gas. Natural gas comes out of gas wells and petroleum wells. It contains about 60 to 95% methane with small amount of other hydrocarbons. It is to be transported through pipe lines for a long distance, this increases the cost of plant.
- They have more advantages than oil fuels. But the difficulty is that they cannot be stored easily as oil can be stored. Hence, it is necessary that power plants be installed near the natural gas field.