Steven Meyers, Wood Purchasing Manager, Fram Renewable Fuels and Malcolm Swanson, President Astec Inc., discussing progress at the Hazlehurst site. A few items are not from Astec, wheeled loaders (Volvo), five hammermills (Schutte Buffalo) and inside the building being clad to the right are four Kahl 6 MTPH pellet presses undergoing hot-commissioning. Bioenergy International PS1 2015 17 yard on the feedstock side and by the post-press conveying to storage and loadout silos. –This means there are very few points in the process where any equipment failure can shut the entire plant down. In the 60 TPH plant, a dryer outage and the plant continues to operate at 40 TPH. Major maintenance cycles can be performed line-by-line while the plant continues operating the other lines, explained Swanson. Another major benefit, apparent at Hazlehurst, is that most components arrive on site assembled ready to drop into operating position which facilitates fast set-up and revenue generation. Equipment placement at Hazlehurst began in July 2013, rain had delayed some foundation work. By the end of 2013 the first of three 20 TPH pellet production lines commenced hot-commissioning although not everything has been set-up yet. –As you see the logyard with the receiving and chipping set-up has yet to be installed. It will in tandem with the other two production lines. We manage to source and secure most of the feedstock we need for this first line locally as woodchips. There are many wood processors around here and is one of the reasons for us locating in Hazlehurst, said Steven Meyers. VOC control without RTOs The concept uses a two-stage dryer system, first a pre-dryer and then a hot oil tube dryer, which has been specially developed by Astec for pellet production. With no firing in the dryer, it generates its own inert atmosphere of almost 100 percent steam with no oxygen to support possible combustion unlike air-swept rotary dryers. –Hot oil from our Heatec Convectec heater runs through tubes inside the rotary dryer to produce heat for the woodchip drying process, Swanson said. The design enables very precise temperature control capability and can be operated co-current or counter flow at the flip of a switch. Also the amount of volatile organic compounds (VOCs) released from the woodchips during drying are minimized, since the dryer does not use very high temperatures. –That’s a major environment issue and cost item in the wood pellet industry, said Swanson, conventional VOC control in the US typically involves capital investment into regen- (Above) View from the hot oil tube dryer, specially developed by Astec for pellet production. Intermediary storage silos for dry, milled material. (Below) Storage silos for finished product. erative thermal oxidizers (RTOs) which need additional fuel to operate. –All the off-gases from both the pre-dryer and hot-oil dryer are fed into our Heatec Convectec heater, destroying any VOCs while recovering the heat. This means we can build large pellet plants like Hazlehurst without the need for costly RTOs, explained Swanson. The boiler is fitted with a multifuel burner system that can use wood dust alone, or together with off-gasses, gas, oil or liquified petroleum gas (LPG). Apart from fuel flexibility a key advantage is it enables quick plant startups and shutdowns. –Plant startups can go from dead cold to producing pellets within as little as two to three hours compared to other burner systems that may take all day, said Malcolm Swanson. While the focus for Astec is on entering the “white” pellet technology space, the company has an eye on torrefied pellets. Tests have been carried out at its Chattanooga pilot. Time will tell if another first-of-a-kind plant is to become a feature on these pages. Text & photos: Alan Sherrard PS1/4709/AS PELLETS
Bioenergy nr 1 - 2015
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