TECHNOLOGY
Continuous Cold Soda Pulping Scales Up Black-Clawson pilot plants new process for hardwoods, focuses spotlight on steep growth curve for cold soda route Hoping to take advantage of the boom developing for cold soda pulping of hardwoods, Black-Clawson's Pandia division has come up with a new, continuous system it calls Chem Preg. The system is now going through its pilot plant paces at the company's Middletown, Ohio, plant. Chem Preg's chief advantages, according to Black-Clawson, are those for cold soda pulping in general: low power consumption, relatively high yield, low chemical needs, low capital investment. With it, you can produce pulps with characteristics from strength grade to ground wood grade. The process, say the company, will produce a well defîbered pulp at about 12 to 25 hp. per ton, including disk refining. Croundwood, a strictly mechanical process, produces pulps similar to some grades of cold soda pulp, but eats up 70 to 125 hp. per ton. Black-Clawson*s newly designed defibering machine—Chemifiner—has been incorporated into the Chem Preg system, helps to keep power requirements low, the company says. With its high yield of 85 to 95 r/r, Chem Preg also has an advantage over
neutral sulfite semichemical pulping, whi'ch can also be used with hardwoods but gives a yield of only 60 to 80r/c, Black-Clawson says. Furthermore, it needs a large amount of steam for digesting, whereas the cold soda pulping process runs at room temperature. But the new system, its developers point out, goes a step further, also gets around a major problem of other cold soda systems: Wood chips are exposed to chemicals longer on the outside than on the inside. To get a uniform pulp with good fiber length, says Black-Clawson research engineer Paul Marsh, you have to penetrate the wood chips uniformly. Compress, Then Expand. Key to Chem Preg's uniform penetration is a cylindrical section of piping called a plug pipe, located at the small end of a tapered-throat screw press. The screw feeds chips down the tapered throat, compressing them somewhat, then rams them into the plug pipe. This gets rid of air in the chips, Mr. Marsh explains. When the chips come out of the plug pipe, they discharge directly into
caustic soda. With compression released, they expand into an open, spongelike form, are completely impregnated with chemical. Here's how this fits into the process. Wood chips are briefly submerged in liquor squeezings, drained, and fed to the first press. This press squeezes the chips to 65 to 75f/f O.D. (oven dry) in the plug pipe, and they expand into a slightly inclined reaction tube. The inclined tube keeps chips submerged in liquor, which Hows through the reactor at a concentration of 20 to 40 grams per liter (depending on the amount of treatment wanted). Excess liquor flows into a recirculation tank, where make-up is added from a tank of fresh caustic before the liquor recycles to the reactor. Chips can remain in the reactor for 5 to 65 min.; normal treating time is about 20 min. A screw conveys the chips through the liquor in the reactor to the top of the tube, where they drain and drop into a second screw press at about 35f.'f O.D. This press, similar to the first, squeezes the chips to 60 to 65r/< O.D. Squeezings drop into a tank and are used to wet chips at the
BLACK-CLAWSON PROCESS DEPENDS ON PLUG PIPES, CHEMIFINER Wood Chips
Recycle Squeezings Squeezings to Sewer Plug Pipe
1st Press Plug Pipe Cold Caustic JVIake-Up
J
2nd Press _ 48
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Water or Other Diluent
Mixing Conveyor
Chemifiner (Defibers the Pulp) Pulp to Standard Refining
Cold Soda Pulping Moves Up Fast
Here's what it costs to make one ton of cold soda pulp . . . Manufacturing Costs
TOTAL PULP
Wood—Aspen (a $20 per cord; pulping yield of 90%
$22.22
C h e m i c a l s — 5 0 % caustic (a $2.90 per cwt.
UNBLEACHED SULFITE
(anhydrous basis) + $0.60 freight
4.06
Power—540 kwh. (a, $0.01 per kwh.
5.40
Water—20,000 gal. (rr $0.10 per 1000 gal.
2.00
TOUNDWOOD L a b o r — 4 man-hours (a $2.00 per man-hour
Total
8.00
TOTAL SEMICHEMiGAL
41.68
Fixed Costs (100 ton-per-day mill, 90% of capacity) D e p r e c i a t i o n — Ι Ο years, straight line, on total investment of $2,250,000
6.85
Charge on Working Capital—6% on total requirement of $1,450,000
Total
2.65
9.50
Total Direct Cost
51.18
Overhead © 10%
5.12
Total Mill Cost per Ton of Pulp Source:
$56.30
Diamond Alkali estimates Source: Paper M\U News, Department of Commerce
start of the Chem Preg process. Chemifiner. At this point the Chemifiner swings into action. The machine, explains Mr. Marsh, consists of two vertical plates or disks which ro tate at about the same speed and in the
PLANT PILOTS COLD SODA. Black-Clawson studies its continuous cold soda pulping proc ess in this pilot plant at Middletown, Ohio. The plant is available for pilot runs on specific wood types, B-C says
same direction. However, the plates, which have teeth on their faces, are offset, thus produce a speed difference at a given point. It's this speed dif ference, says Mr. Marsh, that disrupts the chips into fibers. And the plates
can't touch, so all the energy goes into defibering the pulp. Before the chips are fed from the second press to the Chemifiner, water is added in a mixing conveyor to re duce consistency to 25 to 35(U O.D.
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Steam is also added to the stock to raise temperature to 120° to 160° F. High density and high temperature add to the machine's efficiency. Following the Chemifiner, water is again added to the stock to take it down to 5 to 10r/r O.D. From here, it is processed the same as any other pulp, depending on the final use. Pollution Problem Is Small. The system shouldn't present too much of a stream pollution problem, BlackClawson points out. Higher yield means less effluent than from other
processes. And in preliminary tests, according to Mr. Marsh, b.o.d. of the effluent turned out to be only around 40 lb. per ton. Furthermore, if the system is used along with a kraft mill, the effluent can be handled by that mill's waste recovery system. The pilot plant will be used for de veloping further improvements in fullscale mills, which are now available. It is also available for pilot runs on specific wood types from any mills in terested in the process, Black-Clawson adds.
More Paper Mills Turn to Cold Soda Pulping
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With standard pulping processes growing slowly but steadily with the pulp and paper industry as a whole, cold soda pulping is a standout. Starting from scratch only four years ago, it is expected to process 300,000 tons in 1960. Although this is only a small part of the total 26 million tons of pulp to be consumed this year, its growth is "phenomenal" compared to the growth history of other processes used by the pulp and paper industry, says Diamond Alkali. Diamond has just completed a study of the cold soda process. Why is the process catching on? Because it can handle hardwoods with high yield and low capital investment, says Diamond. Pulp properties are most similar to those from groundwood processing, but high power re quirements needed to grind wood mechanically limit this process mainly to softwoods. Furthermore, Diamond says, hardwood pulp quality from this process usually isn't satisfactory. On the other hand, most of the chemical processes—acid sulfite, neu tral sulfite, chemi-groundwood, kraft —have been used with hardwoods. However, it costs about twice as much to produce pulps with these processes using hardwoods as it does with soft woods, according to Diamond. Cost for cold soda on the same basis: about $55 a ton. Hardwoods. Fast growth should continue, too, since the major motiva tion behind cold soda pulping is utili zation of hardwoods—and hard woods are coming more and more into the industry picture. In the U.S., Diamond finds, hardwoods have taken over about half of the forest area. For
the pulp and paper industry to keep expanding at its current rate, it will have to use hardwoods more and more. This, says Diamond, is espe cially true in the northeastern and southern sections of the country. Another reason for using hard woods. Hardwoods are hardier than softwoods, thus infest softwood for ests. Either you use them, or you keep clearing them from reforested softwood areas—an expensive opera tion. First use of pulp from the cold soda process was as a substitute for soft wood groundwood pulps. But, says Diamond, with processing more flex ible now, it's possible to make much wider use of the pulp. Today its ap plications include preparing furnish (pulp mixture) for printing paper, newsprint, foodboard, corrugating medium, insulation board, and paperboard. Ten Years. Cold soda pulping was developed about 10 years ago at the U.S. Forest Products Laboratory in Madison, Wis. However, Diamond points out, it wasn't until 1956 that the first full-scale commercial facility began operating. Then, Gould Paper, Lyons Falls, N.Y., installed a plant to make 60 tons a day of cold soda pulp for high quality groundwood printing papers. Today there are about 15 installa tions in the U.S., Europe, Australia, and South America. Some of these: Champion Paper & Fibre, Stone Con tainer, Bowaters, Kimberly-Clark, Dia mond National, and American Boxboard. Foreign operations include: Australian Newsprint Paper Mills, Boyer, Australia, and Vita Mayer Co., Milan, Italy.
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Plastic coated fertilizer capsules may
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