The briquetting process is a little more tolerant of moisture levels than pelletising for instance, but you need to be a fair way down from the levels in green chip. Too much moisture causes problems because when the briquettes are compressed by whatever means, the moisture turns to steam and expands - blowing the briquettes up in the process!
I would also think that chip may be a bit coarse on its own - you'd need some finer materials in there as well to get it to bind properly. It's the lignins and resins etc in the wood itself that are softened by the heat generated by compression - around 80 tons per square inch if memory serves - and these basically glue the briquette together.
I looked at an Indian built machine a year or two back which worked on a piston compressor rather than a hydraulic press or screw extruder - the installed cost would have been in the region of £45k. Fantastic piece of kit though - looked like "Old English" engineering - all huge lumps of cast iron and massive bearings with two half ton flywheels - not like these modern Euro jobs all encased in sheetmetal cabinets with buttons and lights and computer links to the manufacturers etc! It was pretty basic but very durable by all accounts - not like the screw extruders where the plants have welders working full time repairing the screws - they sometimes only work for an hour before they're knackered and need re-facing! They will also work with chopped straw, bark, nut shells, rice husk etc etc.
Cheers,
Andy
