PULP AND PAPER TERMINOLOGY



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PULP AND PAPER TERMINOLOGY





TYPICAL EQUIPMENT NOMENCLATURE PULP AND PAPER INDUSTRY.





BARK HOG—a machine for breaking up bark into small pieces suitable for delivery to the fuel spouts of a bark-burning boiler; typically, a hammermill.


BARKING DRUM—a large drum (typically 10-15 ft in diameter by 45-80 ft long) mounted to rotate on a horizontal axis; designed to receive pulpwood logs at one end and tumble them until the bark is removed by abrasion, discharging them at the other end; also called a de-barker or barker.


BLEACH PLANT—a facility designed to receive pulp from the pulp mill and whiten it to the desired degree for its intended purpose; typically consists of towers, washers, chemical preparation units, pumps, tanks, piping, etc. all designed, to form a workable system for bleaching pulp; will utilize such chemicals as chlorine, chlorine dioxide, sodium hydroxide, sodium hypochlorite, oxygen, etc.; usually consists of several bleaching stages, each one followed by a washing operation to remove color and spent chemicals from the previous stage.


BLOW TANK—a vessel used to receive pulp discharged from a digester and to reduce the pressure level to atmospheric; the blow tank may have provisions to allow the incoming pulp to be fragmented into fibers and to collect the steam as an energy-conservation measure.


BLOWDOWN DRUM—a cylindrical tank that receives blowdown liquid discharged from a boiler; most boilers have a blowdown system that removes solids that settle at the bottom of the lower drum; this system may discharge continuously or intermittently.


BOILER—a large installation designed to produce steam; typically consists of a furnace, steam generator, and wide range of auxiliaries installed in a large building; three general types are found in the paper mill: (1) a bark boiler utilizes bark as its fuel; (2) a power boiler will burn oil, coal, or natural gas as fuel, sometimes in combination with each other or with bark, and (3) a recovery boiler burns the spent black liquor as fuel, recovering the noncombustible chemicals for processing and reuse; the steam generator consists of two horizontally mounted drums and a set of tubes running vertically between them; the unit is filled with water to approximately the middle of the upper drum, and hot gases are passed between and around the tubes, thus heating the water and forming steam, which is collected above the water level in the upper drum; as steam is used, it is replaced with feed-water, which is introduced into the lower drum; auxiliaries are provided to treat the feedwater, provide an adequate air supply for combustion, cleanse the exhaust gases as required, and to operate and control the entire system.


BREAK—an interruption in the production of paper on the paper machine; the sheet has broken and is being dumped into the pits below the machine to be repulped and reused in the process; to restore operation, a narrow strip or "tail" is cut and threaded through the rope run to the dry end, and gradually widened to full sheet width.


BREAST ROLL—the roll that supports the headbox end of the four-drinier wire; driven by friction with the wire.


BRIGHTNESS—a measure of the percent of light reflected from a sheet of paper or pulp; commonly called GE brightness based on the use of scales and instruments marketed by GE; typical values range from 70 for newsprint to 90 for high quality book and printing papers; brightness measurements are made by comparison with standard specimens.


BROKE—pulp that has been through the paper machine (or part-way through) and for some reason was not finished and shipped; typically consists of material released from a break on the machine, trim from normal operations, unsalable quality paper, etc.; normally, this paper is repulped and returned to the process as broke.


BROWNSTOCK—the unbleached pulp as it passes through the pulp mill.


CALENDER—a set of rolls located at the dry end of the paper machine and designed to smooth the sheet; commonly arranged in a vertical stack with two to ten rolls forming many nips through which the sheet passes; the bottom roll, called the king roll or the roll above it (the queen roll) is driven and the rest of the rolls are turned' by friction with the paper and each other; this provides some slippage that tends to smooth the sheet and make it glossy.


CAUSTICIZER—a tank designed to provide reaction time and intimate contact between the chemicals used to form white liquor; the basic reaction in the causticizer is the interaction of calcium hydroxide and sodium carbonate to form sodium hydroxide and calcium carbonate; usually, several causticizer tanks are connected in a series and the reacting chemicals pass through each tank in sequence, providing time to complete the chemical reaction.


CHEST—an agitated vessel designed to hold pulp at various degrees of consistency and stages of processing; may be rectangular or cylindrical, and may have an open or closed top; usually constructed of tile or concrete; may have interior liner for corrosion protection; chests are usually located between processing stages as temporary stora-ge to smooth out the flow of pulp through the mill; commonly used "to hold broke, blend stocks into a furnish, supply stock to a paper machine, store bleached pulp, etc.; vessels designed for storing white-water are more commonly called tanks and do not have agitators,

CHIPPER—a machine designed to reduce logs into chips; consists of a rotating disc or drum with knives set into it and a means of feeding logs to the rotating knives; cuts logs into match book size chips; usually a large machine mounted in a permanent location and fed continuously by a conveyor; smaller units, usually the drum-type, can be mounted on vehicles and used to chip brush, log ends, and trimmings, either in the forest or in urban areas for trash removal; small units (sometimes of the hammermill type) are commonly used in the woodyard as "re-chippers" to process oversize rejects from the main stream.


CLARIFIER—a large tank, usually circular and of concrete construction, designed to allow settlement of solid materials suspended in water; can be rectangular in some cases; typically fitted with a rotating rake that scrapes the settled materials on the bottom to a central point for removal as a solid waste; may include pumps, tanks, piping, and instrumentation for introduction of chemicals to aid settlement of solids; used to clarify raw water for use in a mill, also to clarify waste-water discharged from process operations.


CLEANER—a cone-shaped device designed to remove dirt and other undesirable material from stock; commonly operates on the centrifugal force principle in which the heavier particles are driven to the walls and fall out the bottom while the lighter materials pass out through the top; can be used in applications where the impurities are either heavier or lighter than the stock; typical installations will have a set of vertical cleaners connected in parallel for high capacity stock cleaning.


COATER—a machine designed to apply a coating to the sheet of paper; can be installed on the paper machine and apply the coating as the paper is being manufactured or can be a separate machine with a system for unwinding the roll, passing the sheet through the coating substance, drying the sheet, and then rewinding it into a roll; coatings can be applied by spraying or forming a "puddle" through which a loop of paper passes, receiving the coating on both sides.


CONSISTENCY—the amount of fiber in a given amount of stock; commonly expressed as a percentage based upon weight; typical formula: R = weight of fiber x 100 where the weight of stock ' weight of the fiber may be either its oven dry weight (no moisture) or its air dry weight (approximately 10 percent moisture); the basis for the consistency measurement must be specified and all calculations and instrument calibration must be in conformance with the specifications.


CONVERTING—transforming the basic roll of paper into a salable consumer product; includes cutting,- printing, coating, shaping, folding, forming into a desired product, and packaging for distribution to consumers; converting is usually done at a different location from the paper mill; some paper companies have found it convenient to build converting plants near their paper mills to reduce the transportation costs for basic roll stock.


COOLING TOWER—a structure designed for air cooling of hot liquid; as used in the pulp and paper industry it is a vertical tower/ usually square in cross section, with wooden slats on all four sides, and designed for spraying hot water at the top, allowing the descending water to exchange heat with a rising column of cooler air.


CORRUGATING MEDIUM—a type of paper commonly manufactured especially for use as the corrugated center section of box-board or container board; frequently manufactured by the NSSC process and called "nine-point" from its nominal thickness of 0.009 inch; manufactured in rolls like other ( papers and bant into characteristic curved shape in a converting plant, where the two outer layers are glued to the middle of the upper drum, and hot gases are passed between and around the tubes, thus heating the water and forming steam, which is collected above the water level in the upper drum; as steam is used, it is replaced with feed-water, which is introduced into the lower drum; auxiliaries are provided to treat the feedwater, provide an adequate air supply for combustion, cleanse the exhaust gases as required, and to operate and control the entire system.


COUCH PIT—an open chest located beneath4the couch' roll; designed to receive the entire flow of stock from the wire in case of a break in the wet sheet between the fourdrinier and the press section.


COUCH ROLL—the roll that supports the end of the fourdrinier opposite the headbox; usually a suction roll; on earlier vintage machines, the couch roll was the main drive roll for the fourdrinier and also the place where the wet web was separated from the wire for transfer to the press section; this term is derived from the word couch (pronounced cooch) meaning to separate the sheet of paper from the forming screen; in more recent vintage machines, the wire is driven by an additional roll, the wire turning roll, which is placed below and beyond the couch roll, and the couch roll turns by friction with the wire; with this arrangement, a pick-up roll transfers the wet sheet to the press section.


DEAERATOR—a tank used to remove entrained air from a process fluid; two basic applications in the pulp-paper industry (1) in the stock preparation area, the deaerator removes air entrained in the stock before it is delivered to the fourdrinier, (2) a tank used in the boiler feedwater system to deaerate the feed-water; acts as a direct contact heat exchanger using steam to heat the feedwater and strip out dissolved gases such as oxygen and carbon dioxide, which are vented from the tank.


DECKER—a machine designed to thicken pulp by forcing water to pass through a screen; typically, it consists of a rotating, horizontally mounted drum with the screen as its cylindrical surface and a vat to hold the incoming thin stock; as the drum rotates, the pulp clings to the screen and the water is drawn through the screen by a vacuum suction system within the drum; the water thus removed falls down through barometric legs and is collected in tanks; the decker will have provisions to remove the thick stock from the screen and discharge it into a suitable vessel; many variations are used for different applications and called by various names, such as thickener, save-all, drum filter, or pulp washer; when used as a washer, the machine is fitted with showers that spray water over the pulp on the drum, thus cleansing it of impurities; the operating principle is similar to that of the cylinder-type paper machine formerly in general use, but now usually replaced by the fourdrinier machine.


DIGESTER—a digester is a vessel in which wood chips or other raw materials are cooked to produce pulp; most modern digesters have a continuous feed and continuous discharge of pulp; a typical modern continuous digester is a pressure vessel approximately 200 feet tall and 15 feet in diameter, complete with provisions to supply wood chips, cooking liquor, and steam continuously, and to maintain ^proper operating conditions (temperature, pressure, and cooking time); older digesters (still in widespread use) operate on a batch basis, usually have several digesters in a set with staggered operating cycles to provide a reasonably steady flow of pulp.


EVAPORATOR—in general, a device designed to thicken a fluid by causing water to evaporate; in the paper industry, the kraft process uses a multiple-effect evaporator to concentrate weak black liquor (about 15-20 percent solids) from the cooking process to strong black liquor (50 percent solids); usually has five or six large vessels called bodies or effects, each operating at a successively higher temperature and pressure in the liquor flow direction; steam heats the highest temperature body and flows through each successive body in the opposite direction to the liquor flow.


FAN PUMP—a large, high capacity pump designed to supply stock to a paper machine; typical capacity is 50,000 gpm at 0.5 percent consistency; commonly called "primary" when used to supply the base sheet of a two-ply sheet and "secondary" for the top liner.


FELT—an endless belt of woven cloth material that contacts the sheet as it passes through the paper machine; felts serve as guides, cushions, and drying media for the wet sheet; the various felts used in the paper machine are commonly called machine clothing; generally used in the press and dryer sections of the machine; woolen or synthetic material is commonly used in the press section, while cotton or synthetics are used in the dryer section.


FOURDRINIER—specifically, the wet end of a paper machine that uses a moving endless belt of wire mesh to form the sheet; more generally, applied to the entire paper machine that incorporates the fourdrinier wire belt for sheet formation; named for the promoters who sponsored the development of the endless belt paper machine; most paper mills now use this type of machine; the older type, called the cylinder machine (see • DECKER), has been replaced by the fourdrinier machine in many applications; in the fourdrinier machine, the speed of the wire is varied with the speed of the stock spouting from the head box slice to achieve the desired type of sheet formation.


GRINDERS—large machines designed to produce groundwood; typically consist of rotating wheels with stones attached or imbedded in them; driven by large electric motors rated in thousands of horsepower; operate by having logs pressed against the stones such that the wood is abraded into fiber.


HEADBOX—a box-shaped vessel mounted above and ahead of the fourdrinier and' containing the slice that delivers stock to the fourdrinier wire; extends over the full width of the wire; designed to control the flow of stock at a uniform rate across the fourdrinier; may have internal rolls, baffles, and other devices designed to prevent flocculation and to smooth out the flow of stock in the machine direction; may have pressure controlled by an air pad or other means.

KNOTTER—a device designed for removing knots from pulp; typically, a perforated plate or screen placed in a stock line sized to pass stock but to retain large pieces such as knots.


MECHANICAL PULP-a type of pulp produced by mechanically separating the fibers in the wood, as opposed to the use of chemicals to perform the fiber separation as in chemical pulps (sulfate, sulfite, soda, etc.). The mechanical separation can take place using the following processes:

1. Stone groundwood (SWG). Barked logs are forced lengthwise against a rotating horizontal artificial stone. Power applied per stone can vary between 2,000-10,000 horsepower ,

2. Therm-mechanical (TMP). Chips from barked logs are refined in pressurized revolving disc refiners. Refiner horsepower can vary between 1,000 horsepower to 14,000 horsepower,

3. Chemical thermo-mechanical (CTMP). Same as TMP except that the chips are given a mild chemical pre-treatment ahead of the refiners.

4. Refiner mechanical (RMP). Same as TMP except that the refining is done under atmospheric pressure.


NEWSPRINT-the type of paper used for printing newspapers; commonly made from a blend of mechanical pulp and bleached chemical pulp.


NIP-the line of contact between two rolls'that apply pressure to a sheet passing between them; also the line between two wires used to form a wet sheet; nip pressure is measured in pounds per linear inch along the nip line; typical values run from 100 to 1200 Ib/in, usually increasing in the machine direc tion (for example, 1st press--250; 2nd press--350; 3rd press-- 800). - o>


NSSC PROCESS-the neutral sulfite semi-chemical process for making pulp; uses a bisulfite as the principal cooking chemical; can be sodium, calcium, magnesium, or ammonium bisulfite in pH range of 6 to 9; the carbonate and possibly the hydroxide of the same radical may be present in the cooking liquor; commonly used for producing "nine-point" for use as corrugating medium.


OPACITY-the property of a paper that prevents printing from showing through on the other side; the opposite of transparency.


OVEN DRY — containing no moisture; 100 percent fiber; achieved by exposing pulp or paper samples to elevated temperatures (approximately 215°F) in a dry atmosphere; frequently called "bonedry"; oven' dry is term preferred by TAPPI.


PICK-UP ROLL—the roll that separates the wet sheet from the fourdrinier; located between the couch roll and the wire turning roll on the sheet side of the wire; has internal suction and is covered by a continuous felt that provides a convenient and reliable method of transferring the wet sheet to the


PRESS—a set of two or more rolls designed to squeeze water out of the wet sheet; may have perforations and internal vacuum to withdraw water by suction; some presses are designed for smoothing of the sheet or application of surface treatments; may be driven by an electric motor or differential drive, or may be turned by friction; the line of contact between rolls is called a "nip"; many special names are used for presses, such as suction press, pick-up press, size press, smoothing press, multi-nip press, etc.




PRESS SECTION— usually used on high-speed machines (1500-3500 ft/min) and on lightweight papers ranging from tissue to newsprint to coated book and graphic papers. .


PULP — slurry of wood fibers (cellulosic material) suspended in water; this term is usually applied to the pulp in the pulp mill area — digesters, washing, screening, and bleach plant; when it passes into the paper mill area (stock preparation and paper machine) , it is generally called stock or stuff.


PULPER—a large tank, usually rectangular and of tile construction, designed to re-pulp paper or dry pulp; fitted with one or more agitators to reduce the incoming material to pulp with a consistency suitable for pumping and return to the process; most mills will have pulpers in the basement at the dry end and under the presses or at other strategic locations for recovering broke; also made in cylindrical and tub-shape and used to re-pulp bales of pulp (off-machine service).


REFINER—a machine consisting of large discs, some stationary, some rotating, between which the pulp passes for frictional treatment to break up fiber bundles and release individual fibers; refining is .also performed by jordans (primarily in older mills).


REJECTS — pulp or stock that is not acceptable for use in the machine furnish; commonly rejected at the screens or cleaners and returned for further processing.


ROLL—a term with two general types of meaning in the pulp-paper industry: (1) a roll of paper manufactured by the paper machine and wound up on the reel; typical rolls of liner-board can be-more than 25 feet wide and 9 feet in diameter, and weigh in excess of 10 tons; (2) a metallic cylinder mounted horizontally and used to smooth, press, dry, or • otherwise process the wet (or semi-wet) sheet of paper being manufactured; most rolls have a fixed diameter across their entire length, however some rolls (called "controlled crown") are designed to be expanded or contracted in diameter to accomodate deflection at the center and achieve constant pressure across the nip; dryer rolls are heated by -steam, and contact with the sheet causes evaporation of moisture from the paper.


ROPE—an endless band of rope that runs alongside the sheet through the press section and drier section of the paper machine; used to thread a new sheet through the machine.


SALTCAKE — impure sodium sulfate (Na2SO^) ; also called Glauber's salt; used in sulfate process as make-up for lost chemicals; normally delivered to the process in a saltcake tank just prior to injection of the black liquor into the recovery furnace .


SCREEN—in general, a wire mesh or plate with holes sized to pass desirable particles and retain undesirable particles; frequently takes the form of a basket placed in a vessel and located in a stock line; usually made for removal and cleaning when clogged.


SLICE — a horizontal slot in the headbox through which the stock is sprayed out onto the fourdrinier; normally about three or four inches wide and running the full length of the fourdrinier; adjustable in width to provide desired sheet formation.


SMELT — a molten liquid that emanates from the bottom of the recovery furnace; consists primarily of sodium sulfate, sodium sulfide, and sodium carbonate; forms green liquor when dumped into the smelt tank.


STOCK — pulp after it has entered the stock preparation area, where it is processed for delivery to the paper machine; also called stuff by many papermakers.


STUFF BOX — a box-shaped vessel that supplies stock to a succeeding stage at a constant pressure; elevated to achieve the correct pressure at the delivery point; commonly used to supply the suction of a fan pump. ^


SULFATE PROCESS — the pulp-making process that uses sodium hydr- oxide and sodium sulfide as the principal cooking chemicals; also called the "kraft" process because of the strong pulp it produces (kraft = strong in German) ; uses white liquor for cooking and produces black liquor as the spent chemical solution; includes kraft recovery cycle with a recovery boiler and reconstitution of the whdte liquor through the causticizing process; generally operates in pH range of 13-14 with about 12 percent active chemicals in solution.


SULFITE PROCESS — the pulp-making process that uses a sulfite V chemical for the cooking liquor, typically hydrogen sulfite Ap or calcium, magnesium, sodium, or ammonium sulfite or bi-\ sulfite, frequently in combination with the hydroxide, carbonate, or sulfide of the same radical; may be acid (pH 1-4); neutral (pH 6-9); or alkaline (pH 10+); approximately 20 percent of U.S. mills use this process (1970 survey) . Except for special products, the use of this process is decreasing due to environmental problems and limited tech-nology on liquor recovery systems.


TALL OIL—a combination of many organic compounds such as fats, fatty acids, rosin, and rosin acids, all derived from the hydrolysis of wood in the kraft process; many paper mills have tall oil plants for processing the soap from the evaporator into tall oil for sale to chemical plants for further separation into products used in paints, inks, soap, detergents, plastics, adhesives, and many other applications.


TRIM—the width of the finished sheet of paper; also applied to a narrow strip that is cut off of each side during the manufacturing process.


TURBINE — a prime mover, generally driven by steam and designed to drive a rotating machine such as an electrical generator, fan, or pump; consists of a case and set of rotating plates with blades designed for the service.


WASHER — a machine or vessel designed to wash pulp; usually, a machine like a DECKER, but fitted with showers for cleansing pulp on the cylinder; in recent times, a different type called a diffusion washer has been introduced; it diffuses water through the pulp to remove impurities.


WEB—the sheet of paper being formed on a paper machine.


WHITE LIQUOR—the cooking liquor used in the sulfate process; consists primarily of sodium hydroxide and sodium sulfide dissolved in water; formed from green liquor and lime.


WHITEWATER—water with a relatively small amount of fiber, usually too dilute to have a measured consistency (often expressed in pounds per 1,000 gallons rather than percent); commonly used in both pulp mill and paper mill areas.


WIRE — an endless belt of wire mesh upon which the sheet of paper is formed; originally made of metal; typically phosphor bronze, but more recently of plastic; consists of the warp (lengthwise strands) and the shute (crosswise strands) ; the number of strands per inch (called mesh) varies widely, but falls in the range of 40-80 for most linerboard, newsprint, tissue, and book papers . '


WIRE PIT — an open vessel under the fourdrinier; designed to collect water that drains through 'the wire.


WIRE RETURN ROLLS — rolls located below the wire and arranged to guide the wire from the couch end back to the headbox end; some wire return rolls may be motor-drive (frequently, the first such roll) .


WIRE TURNING ROLL — the main wire drive roll on most modern fourdrinier paper machines; located below and forward of the couch roll; this is the roll that is farthest from the breast roll.


YANKEE DRYER — also called "Yankee" or "Yankee machine"; a large steam-heated drum, some 15 to 20 feet in diameter and up to 20 feet wide; used to dry a wet sheet of paper.





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