8.5　Screen and Coal Crusher

8.5.1　Single-stage screen and coal crusher should be provided for the coal handling system of pulverized coal fired boilers.The coal crusher should be provided with a bypass path.

8.5.2　The screen and coal crusher shall be selected in accordance with the following requirements:

1　High-speed hammer or ring crushers without gratings rather than vibrating screens should be used for coal prone to caking and consequent clogging the screen meshes.

2　Heavy-duty ring-hammer or reverse coal crushers should be used for coal with larger hardness or variable quality.

8.5.3　The grain size of coal after screened and crushed shall comply with the requirements of various types of boilers and mills.

1　For pulverized coal boilers，the grain size should not exceed 30 mm.

2　For fluidized bed boilers or CFB boilers，the grain size should not exceed 10 mm.

3　If the boiler manufacturer has specified the grain size of the coal to be fired by CFB boilers，the screen and coal crusher shall comply with these requirements.

8.5.4　CFB boilers should be provided with two-stage coal crusher，with a roller screen arranged before the coarse crusher and a fine screen before fine crusher.

8.5.5　If the grain size of raw coal complies with the combustion requirements of coal mills or boilers，no coal crusher is required.However，the space for installing the crusher should be reserved.If the incoming coal contains a large quantity of large-size coal blocks or impurities，bulk removal devices should be provided.