Dry Kraft Pulping at Ambient Pressure for Cost Effective Energy Saving and Pollution Deduction
Sponsored by the DOE Industrial Energy Efficiency Grand Challenge program, our research team at the Georgia Institute of Technology conducted laboratory studies and confirmed the concept of making wood pulp using a dry pulping technology. This technology is a new process different from any prior pulping technology used in Kraft and CTMP pulping. Three different kinds of dry pulping methods were investigated. (a) Dry Pulping at Atmospheric Pressure: The first one is to dry and bake the pretreated woodchips in a conventional oven at atmospheric pressure without the use of a catalyst. (b) Dry Pulping at Reduced Pressure: The second method is to dry the pretreated woodchips first in a vacuum oven in the presence of anthraquinone (AQ) as a pulping catalyst, followed by baking at elevated temperature. (c) Liquid Free Chemical Pulping, LFCP. The third method is to first remove the free water of pretreated woodchips, followed by dry pulping using a conventional Kraft pulping digester with AQ and triton as additives. Method one: Experimental results indicated that Dry Pulping at Atmospheric Pressure could produce pulp with higher brightness and lower bulk than conventional Kraft pulp. However, tensile strength of the acquired pulp is much lower than traditional Kraft pulp, and their Kappa number and energy consumption are higher than conventional Kraft pulp. By fully analyzing the results, we concluded that wood fibers might be damaged during the drying process at elevated temperature. The main reason for wood fiber damage is that a long drying time was used during evaporation of water from the woodchips. This resulted in an un-uniform reaction condition on the woodchips: the outside layer of the woodchips was over reacted while inside the woodchips did not reacted at all. To solve this problem, dry pulping at reduced pressure was investigated. Method two: To achieve uniform reaction throughout the entire reaction system, the water inside the pretreated woodchips was evaporated first under vacuum condition at low temperature. Then, the dry woodchips were baked at high temperature (120-130 C) at atmospheric pressure. The qualities of the pulp made with this method were improved compared to that made with method one. The pulp shows higher brightness and lower bulk than Kraft pulping. The tensile strength is significantly higher than the pulp made from the first method. Although the pulp is stronger than that of TMP pulp, it is still lower than conventional Kraft fiber. Method Three: The third dry method was done in a Kraft pulping digester at elevated pressure but without free liquid in the digester. With this method, pulp that has almost the same qualities as conventional Kraft pulp could be produced. The screen yield, Kappa number, fiber brightness, pulp strength and pulp bulk are almost identical to the conventional Kraft pulp. The key advantages of this dry pulping method include ca. 55 % of cooking energy saved during the pulping process, as high as 50 wt% of NaOH saving as well as 3 wt% of Na2S saving comparing to Kraft one. By analyzing fiber properties, yields, chemical and energy consumptions, we concluded that the dry pulping method based on Liquid Free Chemical Pulping, LFCP, could be very attractive for the pulp and paper industry. More fundamental studies and scale up trials are needed to fully commercialize the technology. We expect to conduct pilot trials between 12 to 24 months of period if the DOE or industry can provide continual research funding. Based on the technology we demonstrated in this report, several pilot trial facilities in the United States will be available after small modifications. For example, the Herty Foundation in Savannah, Georgia is one of these potential locations. DOE funding for continuous study and final lead to commercialization of the technique is important.
- Research Organization:
- Georgia Institute of Technology, Atlanta, GA (United States)
- Sponsoring Organization:
- USDOE; USDOE EE Office of Industrial Technologies (EE-2F)
- DOE Contract Number:
- EE0003456
- OSTI ID:
- 1049310
- Report Number(s):
- DOE/EE/3456-1; TRN: US201218%%190
- Country of Publication:
- United States
- Language:
- English
Similar Records
Mill Integration-Pulping, Stream Reforming and Direct Causticization for Black Liquor Recovery
Biomechanical pulping: A mill-scale evaluation
Related Subjects
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
42 ENGINEERING
ADDITIVES
ANTHRAQUINONES
ATMOSPHERIC PRESSURE
BAKING
BRIGHTNESS
COMMERCIALIZATION
DRYING
ENERGY CONSUMPTION
ENERGY EFFICIENCY
EVAPORATION
FIBERS
MODIFICATIONS
OVENS
PAPER INDUSTRY
POLLUTION
SCREENS
TENSILE PROPERTIES
WOOD
Pulping
Papermaking
energy saving
cellulose
wood fibers