called “black pellets” caught their eye. Immediately they liked the idea of a pellet that was water resistant and didn’t have major dust issues. They bought the intellectual property around that process, filed additional patents and started developing it with an eye toward using black pellet technology as a substitute for coal or as a co-firing fuel with coal, meaning a less costly conversion at the power plant. To complement the new venture, Zilkha Biomass Energy built a demonstration plant with full size equipment in Crockett, Texas. Clyde PELLETS 22 Bioenergy International No 79, 3-2015 Stearns for one was impressed with the technology and the product. Stearns, an engineer, had worked for years with Globe Machine and its finishing end equipment in the plywood industry, as well as for project fabricator WPS Industries and heat energy and drying systems supplier TSI. More recently Stearns had been the sales manager over biomass and wood pelleting at Buhler, which provided machinery to the Green Circle Bioenergy 650 000 tonne wood pellet plant that started up in 2008 (and which in January was purchased by the large white pellet producer, Enviva). Stearns joined Zilkha Biomass Energy in 2011. Stearns points to the impressive properties of the black pellet – hydrophobic so you can store it outside, low dust, no self-heating, little oxygen consumption, no additives, safe to handle, safe to ship–but emphasizes that the real difference is the higher energy value – a net califoric value of about 19.3 megajoules per kilogram, giving the black pellet up to 15 percent more energy per kg, he says, and a higher bulk density of 15 percent or more. “So when you load a shipload full of black pellets, you have about a 30 percent advantage,” Stearns says. “The combination of the higher energy and the higher bulk density is the big transportation and storage advantage of this product.” Still, it’s the visual image that makes an immediate impression. Successful testing overseas began with a shipment of 4 000 US tons to a power company in Europe. Rain pelted down on the open pellets at the Port of Beaumont (Texas). Zilkha Biomass likes to do the water glass test, where white pellets are put in a glass of water and black pellets are put in another glass, and after an insignificant amount of time the white pellets turn mushy. For all of the above reasons, a utility company in Europe has signed an off-take agreement with Zilkha for the majority of production from the Selma plant. But what makes the “Zilkha Black” pellet black? Zilkha describes its technology as “thermal conditioning.” The wood is put in a sealed pressure vessel, steam is injected, and then steam is released, blowing the fibers out of the pressure vessel, separating the wood into cellulose, hemicellulose and lignin so that lignin is available to act as a binder. And it’s not torrefaction, which is a different process that is also trying to produce a charcoallike pellet. Stearns explains that torrefaction heats up wood in a contained environment in the absence of oxygen. “The challenge for torrefaction has been largely how do you control that process – once you start cooking in the absence of oxygen it’s hard to stop the process and re-introduce the product into an oxygen environment,” he says, adding that the torrefaction process achieves high energy, but you lose a lot of mass (wood weight) and binder to do it. “Our view is there’s a sweet spot where you get the properties you want, higher caloric value, water resistance, with a much lower mass loss. At the end of the day, a technology like ours is a much lower cost producer.” Selma Conversion But a lot had to be done before Zilkha could go commercial with its product, such as doing an overhaul of the former Dixie Pellets white pellet plant. Zilkha and the equipment manufacturer/ supplier, Bruks, worked together to build and pave a new chip yard. They added two new Fairbanks truck scales to supplement an existing Fairbanks scale; added a Bruks truck dumper to two existing Phelps truck dumpers; installed a new Bruks radial chip stacker; expanded the chip storage area; put in a new live bottom reclaimer; new General Kinematics scalping screen; two new Bruks green hammermills for resizing ¾ inch(≈19mm) chips to 3⁄8 inch (≈9,5mm) and which served to increase the capacity of the dryers; and a new chips-to-silo conveyor. Zilkha also purchased a new Volvo wheel loader for moving chips throughout the chip yard and feeding the reclaimer. Two existing MEC single pass rotary dryers were reconditioned and two WTS dual fuel burners added. Two new Hurst 19 000 lb/hr (≈8,6tonne/hour) firetube boilers provide steam for the thermal conditioning. Zilkha operators refer to them as a workhorse boiler that responds faster to turning up and down. After drying, chips come from two dry chip silos up a conveyor and into the thermal conditioning area, the » The thermal conditioning station is where the black magic happens. Consisting of a battery of six reactor vessels it is the pressures, temperatures and exact sequence that forms the proprietary part of Zilkha’s technology. (Bottom right) One of the two existing MEC singlepass rotary dryers that were reconditioned and fitted with WTS dual fuel burners. The two new Bruks green hammermills. Cont. from page 21
Bioenergy no 3 May 2015
To see the actual publication please follow the link above