BioCycle September 2007, Vol. 48, No. 9, p. 43
Material handling improvements at mulch and garden products operation provide valuable insights for any facility grinding, screening and storing woody biomass.

THE 80-acre production yard at the Oldcastle Lawn & Garden Products facility in Quakertown, Pennsylvania is typically loaded from front to back with raw materials and finished mulch and soil products. The day we visited in August, the site was in between seasons. “When we are in full production, the entire site is filled with stacks of materials, from unground and ground pallets on one side to freshly colored and natural mulches and aging ground wood products on the other,” says Bruce Derewal, Production Manager.
In addition to receiving pallets, Oldcastle takes land clearing debris and stumps. “We will not accept construction and demolition wood, however,” he adds. Incoming wood is ground with a Diamond Z tub grinder, then passes through a Re-Tech screen. Overs are conveyed to an electric grinder, then conveyed back to the screen in a continual loop until all the product reaches 1.5-inch minus particle size.
Until four years ago, front-end loaders were used to move screened and/or colored products to storage piles. Loader operators would drive up on the piles to stack materials as high as possible in order to maximize storage capacity. “Driving on the piles would compact and compress the wood products, which creates conditions that may lead to spontaneous combustion,” says Derewal.
To increase storage on the site and prevent fires, Oldcastle (at the time Frontier Wood Products) decided to invest in a telescopic portable radial stacker. The company purchased the ThorStack2, manufactured by Thor Global Enterprises Ltd. The telescopic stacker was initially designed for the aggregate industry. “Regulations dictating material specification requirements in the aggregate industry have become increasingly stringent,” explains Tina Johannsen, whose father invented the first telescopic stacker. “When building a conical pile using a standard radial stacker, the larger aggregate often segregates by rolling to the bottom of the pile, which makes it difficult to meet controlled specifications. The telescopic stacker was designed to build stockpiles in a way that the aggregate remains unsegregated.”
It quickly became apparent that the telescopic stacker had applications in other industries, including wood processing for biomass energy, and mulch and compost production. Reducing fire risk is a key benefit to use of the unit in the wood industry. “When stockpiling with a ThorStack2, the material is being poured under constant motion, which reduces friction and keeps the material loose and aerated, ensuring the core temperature does not rise to the point of combustion,” explains Torben Johannsen of Thor.
Derewal says Oldcastle has clearly benefited in terms of fire prevention. “We haven’t had problems since we began using the stacker,” he says. The company has multiple fire hydrants strategically located around the site. Firefighters have access to water collected in a holding pond at the base of the site.
MATERIAL HANDLING BENEFITS
In addition to fire prevention, use of the stacker has reduced the number of loaders needed to move products around the site. “We were able to relieve our front-end loaders for other purposes,” notes Derewal. “We were operating seven loaders and now we’re down to five.” The unit can be programmed to move front, back and sideways when the stacker senses an area is full. Gaps in between piles can be filled in. “We can stack materials as high as 50-feet,” he adds.
The stacker maintains a constant distance of 1.5 feet from the head pulley of the discharge conveyor to the pile. Sensors are calibrated to detect material at a predetermined distance by emitting sound waves.
Oldcastle recently purchased a Colorbiotics Sahara colorizing unit to increase production of its colored mulch products. Colorized mulches also are stacked by the Thor unit. Nearby on the site, there is a Mighty Giant swing-hammer tub grinder that Oldcastle uses for a second grind on its wood products. “We find the swing hammers are more forgiving when there are contaminants,” says Derewal. The company makes its own blends of topsoils and potting soils. Products are sold both in bags and in bulk. – N.G.