Louisiana Paper Plant Adapts For Biomass

The complete replacement of a fuel delivery system provided a Louisiana paper manufacturing facility with the biomass-based renovation it needed.
By Trotter Hunt
A biomass boiler at a Louisiana paper manufacturing facility was recently renovated. The project included the complete replacement of the fuel receiving, storage and retrieval systems for a wood-fired boiler.

The four-year project began by performing a study of the existing fuel delivery system at the plant. Material handling specialists analyzed the capability of the existing system, identified the bottlenecks and recommended solutions to increase the ability to deliver more fuel to the boiler while providing better storage and material retrieval options.

While there were some gains to be had by modification of the existing system, the long-term solution to meeting the client's desired feed rate to the boiler was a complete replacement of the fuel delivery system. This study formed the basis of a funding grade scope and estimate, which culminated in the client obtaining the necessary funding to proceed with the project.

In addition to the project's detailed engineering, Ruston, La.-based Hunt, Guillot & Associates, through its on-site services division, also provided construction management and start-up expertise to the client's project management team.

The Project's Scope
Hunt, Guillot & Associates was selected to perform the detailed engineering for the new fuel handling and delivery system. As the facility was an existing operation, the site selected for the new system was remote from the boiler, thus necessitating long conveyor lengths to deliver material to the boiler. The design was for the system to be able to process and store 150 tons per hour of incoming wood material, in addition to handling and storing the plant-generated material on a 2 million-cubic-foot storage pile. The storage pile was sized to provide the plant with approximately 10 days of onsite storage, available to be processed and ready for retrieval for the boiler.

The plant's owners stipulated the ability to be able to process a wide variety of incoming quality of materials. The facility was already receiving material from in-woods grinding operations, bark from offsite wood yards, saw mill waste and wood chips. The facility owners believe that as biomass fuel use increases, the ability to receive rougher or less-processed material will allow it to obtain fuel at competitive prices. Engineers successfully designed the receiving system to be able to handle the receipt of materials ranging from finely ground sawdust to blocks 108 inches long. The chains in the oversized truck dump hopper were equipped with a variable speed drive that allowed the unloading time to be decreased when better quality material was received.

Engineers also specified wide conveyor belts with skirted side boards to minimize spillage. Conveyor head boxes were sized to allow the extra length materials the ability to transition between the conveyors. A scalping screen was installed ahead of the grinder. However, the grinder was sized to process the full 150 tons per hour of material. Metal detection and removal capability was designed into the system.

The major components of the system included a new truck dumper, screen and grinder, a circular stacker reclaimer and all of the interconnecting conveyors to supply the biomass to a new fuel bin in the boiler building. The reclaim system was designed to retrieve, weigh and deliver 80 tons per hour of fuel to the boiler, utilizing an over-pile chain reclaimer, and conventional idler belt and air-supported belt technology. The bark reclaim conveyor, at 750 feet long, also provided an emergency feed hopper to allow the plant to continue to feed fuel to the boiler. It also provided a magnet for secondary tramp metal removal and the scale to provide the weight of the material supplied to the boiler.

The 1,250-foot long air-supported belt is one of the longest continuous spans in the country. It was routed through the middle of the operational pulp and paper mill. Air-supported belt technology utilizes a cushion of air to support the belt and the conveyed material on the carry side of the belt. It also uses a cushion of air on the return side of the belt, resulting in a conveyor with only five rollers for its entire length.

The cable tower technology that is utilized to support the air-supported belt allows for a maximum of 250 feet between towers. This allowed the entire 1,250-foot length of the conveyor to be installed with only six intermediate supports between the heat and tail. Use of this technology resulted in substantial savings to the plant in reduced amounts of support steel and installation labor.

Hunt, Guillot & Associates' engineering and purchasing groups issued equipment specifications, proposed bidders lists and inquired the equipment for the plant, supplying bid tabulations and recommending vendors. The project's foundation design included an elevated concrete structure to support the 800 horsepower grinder, the foundation and access ramp for the 75-foot truck dump platform, and the foundation design for the 2 million-cubic-foot stacker reclaimer that was supported on 70-foot deep auger cast piles.

Plant power was received at 13,800 volts at a new electrical control room and distributed to end users. Programmers supplied the necessary programmable logic controllers (PLC) programming to operate the systems, interfaced with other PLC-based systems, designed the graphics for the operator control station and interfaced with the plant's existing distributed control network.

Expertise in construction management was provided to the project management team at the beginning of the construction phase of the project. The primary effort was to provide for coordination of the multiple contractors and sub-contractors involved in the construction, thus ensuring that the project schedule would be met and result in a successful start-up.

An on-site controls engineer and programmer were also provided during the start-up sequencing to immediately resolve any control issues. The efforts resulted in the project being completed with no unplanned operational interruptions to the facility. Start-up was on schedule and done safely.

Trotter Hunt is the relationship manager at Hunt, Guillot & Associates LLC. Reach him at [email protected] or (318) 251-5929.