Cogeneration Plant

[brianJ]

What are the basics to the way these plants buy chips?    I assume by the ton.   Would there be any adjustments for moisture or density of the chips?   Certain size chips or deducts for contamination with mud/dust?   

[Ron Wenrich]

I helped to site a cogen plant a good number of years ago.  We bought a combination of chip and dust.  The prices were cheaper for the fiber.  Moisture content had no bearing, as some of the trash steam was used in the drying process.  Their process used a smaller size, so the chips were reduced to dust.  The dust was blown into the boiler and burnt in suspension.  Not sure what effect there was for dirt, as most mills were running debarkers.  Bark has a higher market value than chips or dust. 

The plant worked this way for a good number of years, but went over to natural gas.  Gas turned out to be cheaper and didn't require any additional handling.  When we sited the plant, gas wasn't a factor in price.  Coal and culm (coal spoils) piles were our major competitor for cogen.  We also looked at sawdust for smaller applications, as it was cheaper and easier to handle.

Other operations may just buy chips.  Depends on the burning technology.  Everything I did on the resource analysis was based on tonnage.