A Fundamental Review of the Relationships between Nanotechnology and Lignocellulosic Biomass - The Nanoscience and Technology of Renewable Biomaterials - page 34

costs by both reducing the amount of energy consumed during processing and capital
equipment required. Nanotechnology applications can take the forms of: nanocata-
lysts to reduce the temperatures and time needed to delignify wood in pulping; low
corrosion nanocoatings and nanomaterials to prolong the life of capital equipment; nan-
odimensional tags/markers for fiber separations; nano-inspired products that help with
water removal on paper machines (drainage wires, vacuum boxes, wet presses, and dry-
ers), kilns, and hot presses; and robust nanodimensional sensors (temperature, pressure,
tensile/compressive forces, etc.) that can be used to monitor and optimize processing
conditions as well as reduce/eliminate off specification product productions; etc.
Fiber, energy, and chemicals rank as the highest nonlabor operating cost items or
categories at most pulp and paper mills. The ratio of costs will vary among different types
of mills, but a typical integrated mill producing 1500 tons of kraft pulp per day will spend
about US$45-60 million for wood, US$30 million for chemicals, and US$15-20 million
for purchased energy each year. Energy reduction goals for pulping and papermaking
are to reduce pulping process energy consumption by at least 33% and produce the same
or better quality fiber at 5-10% higher yield; reduce energy consumed in the process
of increasing black liquor solids (kraft pulping) by at least 50%; develop lower-cost
technology to replace the current (energy and capital intensive) causticizing process;
reduce energy consumed in the paper machine wet end by at least 33%; reduce the
energy consumed in paper dewatering, pressing, and drying by at least 50%; and reduce
energy and produce same or better-quality paper products by using: (a) nanocoating

pigments and (b) three times the nonfiber filler content.
Drying is the most energy-intensive process employed in most pulp and paper mills,
consuming between 4.6 to 9.2 GJ/metric ton (4 to 8 million BTU/ton) of pulp, depend-
ing on the paper grade. The amount of water removed by drying is determined by
the efficiency of the nonthermal water removal processes (i.e., drainage, vacuum dewa-
tering and wet pressing). As an approximation, every 1% increase in sheet solids as
the sheet passes to the dryer section effects a 4% savings in dryer energy use. Paper-
making is a complex operation requiring tight control to produce the expected level
of quality. The huge quantity of water that must be removed and the required level
of precision drive capital and operating costs. Nanotechnology needs for paper and
paperboard drying are to develop cost-effective nano-inspired technologies that reduce
the energy consumed in web/paper/paperboard dewatering, pressing, and drying by at
least 50% via (1) developing next generation one-way water removal wet presses that
employ felts that prevent/eliminate sheet rewetting, allow higher press nip forces, and
extended nip lengths/dwell times to achieve significantly higher solids content of the
paper/paperboard web entering the dryer section and (2) developing next-generation tech-
nologies that improve energy transfer to the web/sheet and water/water vapor removal
for drying.
Energy and chemical usage varies with the pulping processing used. In the US,
kraft pulping (both bleached and unbleached) is by far the largest pulping process
used with over 45 million metric tons (50 million tons) of pulp produced annually.
Semi-chemical, chemi-thermomechanical, Thermomechanical, and refiner mechanical
pulps are employed but the tonnages produced are much, much less. In kraft chemical
pulping, wood chips are heated to 160-180 ◦ C (320-356 ◦ F) at a liquor to wood ratio
of about 3.5 to 1 using sodium hydroxide and sodium sulfide and held for a period of