Grinding Biomass in Coal Grinders 1

[ttwoodbury]

Good morning folks
We are having difficulty with grinding wood pellets in an existing coal grinder. Is there a resident expert that can chat?

Thanks

 

[handleman]

After some additional processing (heat, pressure, time, etc) your wood pellets should become processable in your coal grinder.

-handleman, CSWP (The new, easy test)

 

[muddybiker]

Hi ttwoodbury,

What type of coal mill are you using? Are you milling the wood pellets with coal, or by themselves? I would be happy to help if I can. Depending on the type of mill, there may be some fairly simple adjustments that will improve performance.

Regards,
John

 

[ttwoodbury]

Thanks guys.
It is a verticle, 2 roller mill. We will be slowly blending in wood pellets.

 

[muddybiker]

Vertical roller mills can break the pellets back to their original particles sizes without much trouble, but the classifier will reject the particles until they are finely ground like coal (say 98% passing 50 mesh, 297 microns). The particles do not grind as easily as coal, especially when mixed with coal. The particles will eventually build an inventory in the mill and can overload the grinding table. You will probably notice an increase in mill power and some vibration, which can be severe. The mill throughput will be reduced due to the power increase, vibration, and differential pressure caused by the excessive recirculation of wood particles. De-tuning the classifier will allow larger wood particles to leave the classifier, but at the expense of coal fineness. There is a limit to the amount of wood that can be co-milled for all of these reasons.

Here is a paper that talks about co-firing and co-milling coal and wood pellets:
Link

There are many other articles and papers about this subject out there as well.

Let us know how it goes. I'm interested to hear more about your particular experience.

 

[rogerbours]

Hi there

there is indeed evidence and proof that co-firing biofuel with coal leads to a very much increased risk for dust explosion hazards, especially in the milling part of the plant. There are several studies made and papers presentedd where this is addressed and where the need for dust explosion prevention and protection is highlighted.

Especially when adding more then 10% biomass there is a steep risk increase, this has for example led to the mandatory inclusion of explosion protection measures in many affected power plants in Europe