The following items are common to wood and yard waste recycling operations. Because of the amount of equipment required to recycle all of these items you may see many operators who limit their recycling to only one or two items listed.
Yard trimmings are the easiest to process of all the materials listed and make up for approximately 15% of the total solid waste stream in the United States. They are by far the largest portion of recyclable wood and yard waste materials available. They are generally small in size, less than 2” in diameter, less than 4’ long, and are easy to handle. They consist of grass, leaves, brush and tree trimmings. Tub grinders and horizontal grinders have proven to be the most efficient machines available for processing these materials into smaller particle sizes and into final products.
Long tree limbs are difficult to handle and require grinders with large infeed openings to accommodate them. Tree limbs are normally mixed with yard trimmings so if you accept one you will normally get the other. Tub Grinders type and Horizontal Grinders have proven to be very efficient machines for processing tree limbs into smaller particle sizes. If you have no control over the length of material you receive then you will need a grinder with a large infeed opening. If you have control over the length then you can get by with a smaller machine. You can waste a lot of time and money trying to put long material into a grinder with a small infeed opening. Long lengths of course are relative to the machine in question; 10’ long is okay if the machine is 12’ wide at the infeed opening, 8’ long is okay if the machine is 10’ wide, etc. If you use a tub type machine with an infeed opening smaller than your materials length the material will constantly bridge across the infeed opening and production rate will be less than anticipated. If you have a horizontal feed machine the longer lengths are not a problem, although organizing tree limbs to fit in a horizontal machine can be time consuming. Some customers control the length of material coming into their facilities by requiring that it be cut to shorter lengths. They are then able to save money by utilizing a smaller machine (by smaller I don’t mean lighter duty, just a smaller infeed opening).
It requires an extraordinary amount of work to reduce tree stumps down to chips and remove contaminants, but the small chips do make excellent landscape products. For shredding large diameter wood and stumps you will need either a slow speed shredder or a shear mounted on a large track type excavator. This equipment is used to break up large diameter wood and stumps (over 18” diameter) into sizes which can be processed more efficiently by a hammermill grinder. Since hammermills don’t work economically with rock and dirt you will need to run the broken and sheared chunks of wood across a screen which is capable of removing most of the dirt and gravel previously attached to the stumps. This can be accomplished with either a heavy-duty trommel screen or a flat shaker screen. And finally, you can process the cleaned chunks of wood into small marketable products with a hammermill grinder.
Pallets and construction wood make up approximately 7% of the total solid waste stream in the US and are second to yard trimmings in the amount of raw woody material available for recycling. They are usually processed through a tub grinder along with yard trimmings and recycled into landscape mulch, boiler fuel or sewage sludge bulking agents. Normally, the wood is not large but it can sometimes be long, over 10’. Most grinders handle this kind of wood very easily. The big problem with pallets and construction wood is the amount of non-woody materials that are associated with them and that must be removed from your finished products. Also, wood that is nailed together such as pallets and crates slow down the grinding operation because they create a lot of air space within the infeed hopper. When recycling pallets and crates it is very helpful to pre-grind the material by crushing it with a track-type loader or excavator. If you need to remove nails and other metal from your product, then you can install a magnetic head pulley and/or a cross belt magnet to your grinder (if not already equipped) to remove up to 95% of metal as it exits off the primary discharge conveyor.