Pellet plant optimization and efficiency are multifaceted

By Lisa Gibson | July 25, 2011

Pellet plant efficiency and optimization can hinge on a multitude of factors, not the least of which being raw material variances and the use of proper machinery. Two speakers addressed this topic at the Pellet Fuels Institute Annual Conference July 24-26 in Ponte Vedra Beach, Fla.

In his presentation, Clyde Stearns, vice president of engineering for Zilkha Biomass Energy and biomass and wood pelleting expert for equipment manufacturer Buhler Inc., emphasized minimizing raw material variance. “You have to have really intimate knowledge of your raw material,” he said. Showing a map of the U.S. and the varying available wood types, he explained, “The U.S. is not homogenous at all for wood species.” The external selection of raw material is important, making it crucial for a pellet company to understand the different types of wood it will use, and what form it will be in.

Subsequently, internal homogenization requires constant material supply characteristics. Stearns included in his presentation a fact versus fiction element of pelleting, saying that contrary to popular belief, a complicated and expensive mixing system is not essential in a mixed-species wood pellet plant. A basic system is sufficient, he assured, but chip size and variance need to be relatively uniform.

He also addressed minimizing moisture and equalization in a pellet mill, discussing drying time and predrying. “In an ideal world, I would recommend covered chip storage,” he said. “If that can be done, it dramatically improves the drying operation.”

Stearns also discussed wet material sizing, complemented later by the presenter who followed him. Cole Martin, sales manager at Dieffenbacher Inc., described the company’s two new sizing technologies being used in Europe now.

The first, The Eco Pulser, is a non-contact sizing machine that works through shock waves designed to minimize the wood size, he said. The material is fed into the machine through the middle, and into the counter-rotating motors. Any sand, stone or similar material is powdered, and contaminants such as plastics and metals are detected through frequencies within the process and released for disposal. The system, which has installations in Germany, uses less power than traditional sizing equipment, emits no pollutants and makes little noise, he said. The Eco Pulser, however, is not for absolute sizing.

Dieffenbacher’s ClassiSizer is a better fit for that. While it is an impact sizer, it uses no hammers, knives or flakers, Martin said. The system has been used in wood chip processing and residential wood processing and is breaking into the pellet mill market with one installation already and another in the near future. “It’s used in a number of different industries,” Martin said.

Because there is no cutting of the chips, the system experiences little wear. It is also insensitive to contaminants and is low maintenance. It functions through a rotor that throws the wood at a screen, Martin explained. Some goes through and is sized, while other material comes back to be thrown again. The process requires half the energy a traditional hammermill would and can handle frozen material.

The presentations were crucial for prospective pellet manufacturers, as they offered an excellent overview of efficiency factors and the equipment that can enhance those factors.