A wide range of coals can be applicable to the pulverized coal boilers in power plants.
Highly volatile Lignite and less volatile anthracite can be used in the boilers. But for a boiler that has been installed and in operation, it is impossible to burn coals of various volatilities due to the restriction of burning type and hearth structure.
The quality requirements on the coal used for generating electricity are as follows: firstly, volatility is the primary index for ascertaining igniting characteristics. The more volatile it is, the easier it is to ignite. In line with the requirements on the boiler design, the volatility of the coal used shouldn’t fluctuate too much, otherwise it will affect the normal operation of the boiler. For instance, when the coal of low volatility is replaced by the that with high one, the center of the flame will approach the orifice of the jet burner and probably the boiler will stop as a result of the broken burner.
On the other hand, when the coal of high volatility is replaced by that of low volatility, it will take too long to ignite, which will lead to the incomplete combustion and eventually flameout. Therefore it is advisable to utilize the coal whose volatility is similar to the design volatility.
1.Ash. Ash content will result in the decreased speed of flame propagation, delay in ignition, instability in combustion and the lower temperature of the boiler.
2.Moisture. Moisture is one of the harmful substances. In the combusting process it will absorb large amount of heat and exert more unfavorable influence over combustion than ash.
3.Heating value. The heating value is one important basis for designing boilers. Since coal powder at power plants has strong adaptability, the heating value should be in harmony with what is prescribed in the original design.
4.Ash fusing point. For the temperature of flame center in the hearth of pulverized coal boiler is above 1500℃, coal ash exists in the soft or liquid state.
5.Sulfur content. Sulfur is the harmful impurity in the coal. Although it doesn’t affect the combustion itself, the content is so high as to erode the equipment and pollute the environment. Therefore, the sulfur in the coal for generating electricity should be controlled, generally within the range of no more than 2.5%.