Main Kraft
Latrisha Adan
There the scores stayed, stuck at 10-9 in the third set between two young American teams with a great deal of interest back home and no way of knowing what was happening save for the slow tick of the online scoreboard.
On Thursday in Stare Jablonki, in northeast Poland, it was a bad thing for Harward and DeBerg. In the second set, Denaburg cracked a swing that caromed off the head of DeBerg, the effects of which compounded to the point that, at 10-9 in the third, DeBerg was unable to continue.
Joining Denaburg and Kraft in the main draw out of the qualifier are Savvy Simo and Abby Van Winkle. Already enjoying a wonderful season, with two NORCECA medals, a stunning upset at the Guadalajara Challenge, making it through the qualifier at AVP Huntington Beach, they extended their run in Poland with two wins in the qualifier to punch their ticket to another main draw.
Even with the new faces of Denaburg and Kraft and Simo and Van Winkle, all of whom are 25 years old or younger, in the main draw, and familiar ones in Kim Hildreth and Teegan Van Gunst, who were straight into the main, all eyes for American fans from here on out will be focused on two teams: Trevor Crabb and Theo Brunner, and Chase Budinger and Miles Evans. Entering the season, Budinger and Evans trailed Brunner and Crabb by nearly 500 points in the Olympic rankings.
Regardless of results in Stare Jablonki, the Olympic race cannot be mathematically decided until next week in Ostrava. If Budinger and Evans win gold in Poland and Brunner and Crabb do not add to their total, a gold in Ostrava for Crabb and Brunner would still keep the race tied.
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The kraft process (also known as kraft pulping or sulfate process) is a process for conversion of wood into wood pulp, which consists of almost pure cellulose fibres, the main component of paper. The kraft process involves treatment of wood chips with a hot mixture of water, sodium hydroxide (NaOH), and sodium sulfide (Na2S), known as white liquor, that breaks the bonds that link lignin, hemicellulose, and cellulose. The technology entails several steps, both mechanical and chemical. It is the dominant method for producing paper. In some situations, the process has been controversial because kraft plants can release odorous products and in some situations produce substantial liquid wastes.[1][2][3]
A precursor of the kraft process was used during the Napoleonic Wars in England.[5] The kraft process was invented by Carl F. Dahl in 1879 in Danzig, Prussia, Germany. U.S. patent 296,935 was issued in 1884, and a pulp mill using this technology began in Sweden in 1890.[6] The invention of the recovery boiler by G. H. Tomlinson in the early 1930s was a milestone in the advancement of the kraft process.[7] It enabled the recovery and reuse of the inorganic pulping chemicals such that a kraft mill is a nearly closed-cycle process with respect to inorganic chemicals, apart from those used in the bleaching process. For this reason, in the 1940s, the kraft process superseded the sulfite process as the dominant method for producing wood pulp.[6]
The wood chips are then cooked in pressurized digesters. Some digesters operate in a batch manner and some in a continuous process. Digesters producing 1,000 tonnes or more of pulp per day are common, with the largest producing more than 3,500 tonnes per day.[8] Typically, delignification requires around two hours[9] at 170 to 176 C (338 to 349 F). Under digesting conditions, lignin and hemicellulose degrade to give fragments that are soluble in the strongly basic liquid. The solid pulp (about 50% by weight of the dry wood chips) is collected and washed. At this point the pulp is known as brown stock because of its color. The combined liquids, known as black liquor (because of its color), contain lignin fragments, carbohydrates from the breakdown of hemicellulose, sodium carbonate, sodium sulfate and other inorganic salts.
The weak black liquor is further evaporated to 65% or even 80% solids ("heavy black liquor"[10]) and burned in the recovery boiler to recover the inorganic chemicals for reuse in the pulping process. Higher solids in the concentrated black liquor increases the energy and chemical efficiency of the recovery cycle, but also gives higher viscosity and precipitation of solids (plugging and fouling of equipment).[11][12] During combustion, sodium sulfate is reduced to sodium sulfide by the organic carbon in the mixture:
The molten salts ("smelt") from the recovery boiler are dissolved in a process water known as "weak wash". This process water, also known as "weak white liquor" is composed of all liquors used to wash lime mud and green liquor precipitates. The resulting solution of sodium carbonate and sodium sulfide is known as "green liquor". The green liquor's eponymous green colour arises from the presence of colloidal iron sulfide.[13] This liquid is then mixed with calcium oxide, which becomes calcium hydroxide in solution, to regenerate the white liquor used in the pulping process through an equilibrium reaction (Na2S is shown since it is part of the green liquor, but does not participate in the reaction):
The combination of reactions 1 through 4 form a closed cycle with respect to sodium, sulfur and calcium and is the main concept of the so-called recausticizing process where sodium carbonate is reacted to regenerate sodium hydroxide.
The recovery boiler also generates high pressure steam which is fed to turbogenerators, reducing the steam pressure for the mill use and generating electricity. A modern kraft pulp mill is more than self-sufficient in its electrical generation and normally will provide a net flow of energy which can be used by an associated paper mill or sold to neighboring industries or communities through to the local electrical grid.[14] Additionally, bark and wood residues are often burned in a separate power boiler to generate steam.
Although recovery boilers using G.H. Tomlinson's invention have been in general use since the early 1930s, attempts have been made to find a more efficient process for the recovery of cooking chemicals. Weyerhaeuser has operated a Chemrec first generation black liquor entrained flow gasifier successfully at its New Bern plant in North Carolina, while a second generation plant is run in pilot scale at Smurfit Kappa's plant in Pite, Sweden.[15]
The finished cooked wood chips are blown to a collection tank called a blow tank that operates at atmospheric pressure. This releases a lot of steam and volatiles. The volatiles are condensed and collected; in the case of northern softwoods this consists mainly of raw turpentine.
Screening of the pulp after pulping is a process whereby the pulp is separated from large shives, knots, dirt and other debris. The accept is the pulp. The material separated from the pulp is called reject.
The screening section consists of different types of sieves (screens) and centrifugal cleaning. The sieves are normally set up in a multistage cascade operation because considerable amounts of good fibres can go to the reject stream when trying to achieve maximum purity in the accept flow.
The brownstock from the blowing goes to the washing stages where the used cooking liquors are separated from the cellulose fibers. Normally a pulp mill has 3-5 washing stages in series. Washing stages are also placed after oxygen delignification and between the bleaching stages as well. Pulp washers use countercurrent flow between the stages such that the pulp moves in the opposite direction to the flow of washing waters. Several processes are involved: thickening / dilution, displacement and diffusion. The dilution factor is the measure of the amount of water used in washing compared with the theoretical amount required to displace the liquor from the thickened pulp. Lower dilution factor reduces energy consumption, while higher dilution factor normally gives cleaner pulp. Thorough washing of the pulp reduces the chemical oxygen demand (COD).
In a modern mill, brownstock (cellulose fibers containing approximately 5% residual lignin) produced by the pulping is first washed to remove some of the dissolved organic material and then further delignified by a variety of bleaching stages.[16]
In the case of a plant designed to produce pulp to make brown sack paper or linerboard for boxes and packaging, the pulp does not always need to be bleached to a high brightness. Bleaching decreases the mass of pulp produced by about 5%, decreases the strength of the fibers and adds to the cost of manufacture.
Pulp produced by the kraft process is stronger than that made by other pulping processes and maintains a high effective sulfur ratio (sulfidity), an important determiner of the strength of the paper. Acidic sulfite processes degrade cellulose more than the kraft process, which leads to weaker fibers. Kraft pulping removes most of the lignin present originally in the wood whereas mechanical pulping processes leave most of the lignin in the fibers. The hydrophobic nature of lignin[19] interferes with the formation of the hydrogen bonds between cellulose (and hemicellulose) in the fibers needed for the strength of paper[6] (strength refers to tensile strength and resistance to tearing).
Kraft pulp is darker than other wood pulps, but it can be bleached to make very white pulp. Fully bleached kraft pulp is used to make high-quality paper where strength, whiteness, and resistance to yellowing are important.
The kraft process can use a wider range of fiber sources than most other pulping processes. All types of wood, including very resinous types like southern pine,[20] and non-wood species like bamboo and kenaf can be used in the kraft process.
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