Date: January 16, 1998 (Finalized: May 22, 1998)

Subject: Site Visit--Lenzing Fibers Corporation, Lowland, Tennessee Miscellaneous Cellulose Manufacturing Industry NESHAP EPA Contract No. 68-D6-0012; Task Order No. 0011; EPA Project No. 97/06 MRI Project No. 4800-11

From: Karen Schmidtke

Rebecca Nicholson

To: William Schrock (MD-13) OAQPS/ESD/OCG U. S. Environmental Protection Agency Research Triangle Park, NC 27711

I. Purpose

The purpose of the visit to the Lenzing Fibers Corporation (Lenzing) facility in Lowland, Tennessee, was to develop an understanding of Lenzing’s rayon manufacturing process and the facility’s emission points and emission controls.

II. Place and Date

Lenzing Fibers Corporation Post Office Box 2000, Highway 160 Lowland, Tennessee 37778-2000

November 13, 1997

III. Attendees

Lenzing Fibers Corporation

Dan Blair, Production Manager Calvin Bonawitz, Vice President, Human Resources and Site Services B.B. Bradley, Jr., Project Engineer David Cooper, Environmental Engineer Gunther Krohn, Vice President, Operations William South, Environmental/Auxiliary Service Manager2

U. S. Environmental Protection Agency (EPA)

Bill Schrock, ESD/ OCG, Environmental Engineer

Midwest Research Institute (MRI)

Rebecca Nicholson, Senior Environmental Engineer Karen Schmidtke, Staff Environmental Engineer

IV. Discussion

The site visit included a plant overview discussion, a process overview discussion, a discussion of the emission controls studied, and a tour of the facility.

A. Plant Overview

The site visit began with a general overview of the facility, led by Calvin Bonawitz. Three plants are co-located at the site: (1) Lenzing Fibers (rayon staple production), (2) BASF (idle), and (3) Intercontinental Polymers (polyester production). Lenzing Fibers Corporation is a subsidiary of Lenzing USA Corporation (paren t company), which is owned by Austria-based Lenzing AG. Lenzing purchased the rayon plant from BASF in 1992. The entire facility covers 347 acres and contains a power plant, wastewatertreatment facility, and a landfill. There are approximately 410 employees at the plant (Lenzing employees for rayon staple production). The facility operates 3 shifts per day, 7 days per week. The maximum production rate for the plant, actual production rates for 1997, and the selling price for rayon product are contained in the Confidential Addendum, item 1. Production rate trends are provided in Attachment 1. Attachment 1 is contained in the Confidential Addendum. Facility personnel estimate that the cost to produce rayon staple consists of raw materials (approximately 50 percent), labor, energy, and maintenance services (approximately 50 percent). A breakdown of the cost to produce rayon staple is contained in the Confidential Addendum, item 2. Rayon staple produced at the facility is used in apparel, drapery, nonwovens, and feminine hygiene products.

Rayon processes include filament (one continuous strand) and staple (cut into short lengths). The Lenzing facility uses the rayon staple process. There are two rayon staple producers in the U.S. Domestic rayon production is in tough competition with foreign facilities; therefore, rayon production in the U.S. has been declining.

B. Process Overview and Facility Tour

Mr. Dan Blair provided a process overview and discussion. A general process flow diagram is provided in Attachment 2 and a detailed diagram is provided in Attachment 3. Attachment 3 is contained in the Confidential Addendum. The rayon staple process can be divided into two distinct processes: the chemi cal plant for production of viscose solution and the fiber plant for production of the rayon fiber. The number of process lines is contained in the Confidential Addendum, item 3. The storage facilities, chemical plant processes, fiber plant3

processes, wastewater facilities, currently-used emission controls, other emission controls researched by plant personnel, and modernization projects completed at the facility are discussed

below.

1. Raw Material Storage . Raw material for rayon staple production includes purified, highly reactive wood pulp, sodium hydroxide (NaOH) solution, carbon disulfide (CS 2 ), sulfuric acid (H 2 SO 4 ), and zinc sulfate (ZnSO 4 ). Most raw materials, including pulp and CS 2 , are shipped onsite by railroad. Fresh water for process usage is taken from the Nolichucky River.

The rayon staple process is capable of handling a variety of fiber sources. The facility mixes the type of fiber sources for product optimization. Large rolls of pulp are stored in a warehouse room adjacent to the rayon process (beginning of the chemical process). The rolls of pulp allow continuous feed to the process. Information on the types of wood fiber, size of the pulp rolls, and the plant’s suppliers is contained in the Confidential Addendum, item 4.

Storage of CS 2and unloading of CS 2railcars takes place away from the production area because of the high flammability of CS 2 . Carbon disulfide is stored in six storage tanks; four

tanks contain raw CS 2 and two tanks contain recovered CS 2from the process. The volume of the

CS 2 storage tanks is contained in the Confidential Addendum, item 5. All six tanks are submerged under water in an above-ground water-covered containment pool. This system prevents fire or explosion hazards. If a leak in a storage tank occurs, the CS 2will settle to the bottom (CS 2 has a higher specific gravity than water) and be covered by the “water blanket” in the containment pool. Carbon disulfide is slightly soluble in water, at approximately 2,000 ppm. Additional precautions to eliminate exposure to air or sparks during the transfer of CS 2have been implemented as follows: pipelines from the storage tanks to the process are submerged in water trenches, pipelines for recovered CS 2from the process to the storage tanks are underground, transfer of CS 2 is achieved either by gravity or magnetically sealed pumps, and use of flanges has been reduced where possible. Unloading of CS 2railcars is performed by displacing the CS 2 in the car with water (CS 2has higher specific gravity). The CS 2supplier

handles the CS 2 and N 2gas remaining in the railcar. In addition to submersion under water in the containment pool, the CS 2 within the individual storage tanks is blanketed with water. As the storage tanks are filled (loaded from the railcars) and emptied (CS 2piped to the process), water from the containment pool is added to or displaced from the individual storage tanks. Additional information on the current unloading system for the CS2 storage tanks, a new unloading system to be implemented at the plant, and the total CS2 usage at the plant is contained in the Confidential Addendum, item 6.

Sodium hydroxide is received as a 50 percent NaOH solution and is stored in three large storage tanks. This solution is diluted for use in the process. The volume of the NaOH storage tanks is contained in the Confidential Addendum, item 7.

There are two H 2 SO 4 storage tanks used onsite. The volume of the H 2 SO 4storage tanks is contained in the Confidential Addendum, item 8.4

2. Viscose Solution (Chemical Plant) . The steeping, shredding, and aging steps of the viscose solution process are continuous. The steeping step of the viscose solution process generates alkali cellulose. A Foxboro digital control system (DCS) and an intelligent automation system (IAS) are used for process control of the steeping step. Cellulose pulp is unrolled and shredded into a tank of weak NaOH solution where a liquid solution of the pulp, or slurry, is

made. The concentration of the NaOH solution is contained in the Confidential Addendum,

item 9. This slurry is fed to the mercerization tank, where a sodium atom from NaOH is added to

the cellulose chain. The reaction temperature is contained in the Confidential Addendum,

item 10. (The pulp slurry looks like and has the consistency of applesauce.) From here, the slurry of pulp is pressed or forced between perforated rollers to remove excess water and NaOH. The NaOH solution is recycled. After dewatering, the pulp is shredded and looks like “whitecrumbs.” The “white crumbs,” or alkali cellulose, is conveyed on an aging belt where autooxidation, or natural de-polymerization occurs. The temperature for the aging process is contained in the Confidential Addendum, item 11. The de-polymerization step decreases the viscosity of the alkali cellulose pulp. The length of time necessary for the aging step varies depending on the rayon product or customer specifications. The aged alkali cellulose is the first intermediate generated in the rayon staple process.

The remaining steps for the viscose solution process are batch. The aged alkali cellulose is cooled and is conveyed by air to be weighed and manually charged by dropping through a chute to one of several reactors. Carbon disulfide and a catalyst are added to the reactor and xanthation reaction occurs under vacuum to generate sodium cellulose xanthate. The temperature the cellulose is cooled to, the number and type of reactors, and other process details are contained in the Confidential Addendum, item 12. The reactors are purged with N 2and

vented to remove excess CS 2before opening and emptying following the reaction. Plant personnel indicated that venting of the reactor is an emission point that might also be controlled, given the lower flow and higher concentration of this stream. The xanthation room is ventilated to reduce operator exposure to CS 2 . Carbon disulfide losses from the reactor include conversion to reaction products which later yield H 2 S in the spin bath, volatilization losses sent to the exhaust stack, and the amount remaining in any waste viscose. The sodium cellulose xanthate (looks like orange/yellow crumbs) is the second intermediate for the rayon staple process. Sodium cellulose xanthate is not a stable intermediate and must be processed immediately to prevent conversion back to alkali cellulose. Operation of the reactors is staggered to create a continuous process following the reactor room through the rest of the rayon staple process.

The sodium cellulose xanthate is dissolved in a weak NaOH solution in a dissolving vessel and then is sent to a blending vessel with a high shear mixer to generate viscose solution. The concentration of the NaOH solution is contained in the Confidential Addendum, item 13. The NaOH solution charged to this step is a recycled stream (that has been diluted) from the steeping process above. (Depending on customer specifica tions, titanium dioxide may be added to the viscose solution as a delustering agent.) From the dissolving/mixing vessel, the viscose solution is ripened (i.e., aged) and filtered to produce a uniform solution. Air bubbles and undissolved cellulose that will interfere with the spinning, or extrusion, of the viscose solution must be removed prior to the spinning machine. Filtering and de-aerating are critical steps in the process. The viscose solution is sent to a series of filters before being sent to the spinning machine. The5

filter series is described in the Confidential Addendum, item 14. In the filters, the viscose solution is forced through a metallic mesh. The reject filtrate is composed of undissolved cellulose fiber and is recycled to the dissolving vessels.

A concrete containment area is used as an elementary neutralization tank for wastewater and waste viscose from the aging and filtering operations. Wash water from cleaning of the aging room area is sent to the containment area; these wash waters contain cellulose that must be removed to minimize solids in the wastewater treatment system. Problem batches of viscose, which contain large amounts of cellulose, are also sent to the containment area. The wastewater and viscose streams are neutralized and the cellulose is separated from the wastewater. The separated wastewater is sent to the wastewater treatment system and the cellulose is left in the containment area for later disposal. Disposal of the cellulose sludge is contained in the Confidential Addendum, item 15.

3. Rayon Spinning (Fiber Plant) . Viscose solution is pumped to the spinning machine in the fiber department. The viscose solution is fed to an individual jet and forced through the spinnerette into a bath of H 2 SO 4 solution and ZnSO 4 . A description of the spinnerettes is contained in the Confidential Addendum, item 16. The cellulose precipitates out of the H 2 SO 4 solution and the sodium atom on the cellulose polymer reacts with the H 2 SO 4 to generate Na 2 SO 4 byproduct (sold). (Some spin bath solution is removed from the spinning machine to recover the

Na 2 SO 4 . The spin bath solution is evaporated to increase the concentration of Na 2 SO 4 and the

Na 2 SO 4 is crystallized and removed from the solution.) The ZnSO 4 is added to the spin solution to control regeneration of the cellulose in the spin bath. Exhaust from the spinning machine is vented to one of the main stacks. Carbon disulfide is emitted from the spinning steps, including

the CS 2 exhausted from the spinning bath, stretching, hot dip, and cutting steps and CS 2lost to the spin bath (and later emitted from the bath solution). The area around the spinning machine is

well-ventilated to decrease the concentration of CS 2to which operators are exposed. The spinning machines are partially enclosed for emission control. Information on total enclosure of the spinning machines is contained in the Confidential Addendum, item 17.

The precipitated filaments from the spinning machine are threaded through take-up wheels and onto the first set of rollers. The precipitated filaments are sent through a hot dip bath. Description of the hot dip bath is contained in the Confidential Addendum, item 18. The filament is then taken up on a second set of rollers; the filament is stretched across the hot dip

bath between the two sets of rollers. The stretch is described in the Confidential Addendum,

item 19. Stretching aligns the cellulose molecules in the fiber. Both CS 2and H 2 S gas are released during the hot dip and stretching steps (the high temperature volatilizes these compounds). Carbon disulfide is emitted from the hot dip step; CS 2is volatilized and recovered from the bath by a condenser, some CS 2is lost to the hot dip bath (and later emitted from the bath solution), and a small amount is exhausted to the stack. The recovered CS 2stream is

condensed and returned to the CS 2storage tanks for reuse in the xanthation step (discussed above).

Following the second stretch, the continuous tow filament is cut into various fiber lengths called “chips” (length depends on individual customer requirements) and the cut fiber is6

conveyed by hot sluice water to the wash track and onto a stainless steel mesh belt conveyor. Carbon disulfide is emitted from the belt conveyor and the cutter. The cut fiber is referred to as “dirty cellulose” or “acid chips,” which must be washed and bleached to purify the fiber and generate white rayon staple. Emissions of CS2 from the sluice box are condensed and returned

to the CS 2 storage tanks. The fibers are sent through several washing steps. The washing steps are described in the Confidential Addendum, item 20. The washes used to purify the fiber depend on the rayon product and the customer’s specifications. A finishing spray may also be applied as a lubricant that aids the customer in handling and processing the rayon fiber; these lubricant sprays include oleic acid, mineral oil, or coconut oils. The rayon fibers are pressed through a squeeze roller and sent to the dryer. Moisture content of the rayon fiber is contained in the Confidential Addendum, item 21. The rayon fiber is conveyed through one dryer with three heating zones and a second dryer with one heating zone, a cooling zone, and a conditioning zone. The moisture content for the final rayon fiber is approximately 11 percent. Several physical tests are performed on the fiber, including tensile strength, the elongation, the cut length of the fiber, etc. The dry rayon fiber is packed as 500 pound bales for shipment off site.

There are two cooling towers in use at the plant. The cooling towers are a small source of

CS 2 emissions. The large cooling tower handles water streams from the evaporation step for

Na 2 SO 4 recovered from the spin bath. The small cooling tower is used for water streams from the crystallization steps associated with the Na 2 SO 4 recovery.

4. Wastewater Treatment System . The wastewater treatment system handles approximately 7 to 8 million gallons of water per day; the maximum water that can be processed is 12 million gallons per day. A Foxboro DCS is used to control the wastewater process. Wastewater collected from the rayon staple process contains approximately 20 ppm CS 2 . Wastewater from all sources (including the International Polymers plant and leachate from the onsite landfill) is sent to the equalization basin where mixing of the various influent streams

occurs. The wastewater is then sent to the aera tion basin (where pH is adjusted with lime), two clarifiers, a digester, and a press where sludge is removed. Sludge from the wastewater is sent to the onsite landfill. Water from the wastewater treatment plant is mixed with clear-water lagoon effluent before it is returned to the Nolichucky River through water outfall 001. Storm waters are also collected on the plant site and returned to the river through outfalls 002, S03, S04, or

S05.

5. Emission Controls and Modernization Projects . Carbon disulfide and H 2 S are emitted from the rayon staple process at Lenzing Fibers . Carbon disulfide is emitted from the reactors, spinning machines, stretch rollers and hot dip step, the conveyor and cutters, and the sluice box. Emissions from the hot dip step and the sluice box are controlled by condensers. Because of the toxicity of CS 2 , many areas of the plant where operator exposure is likely are well-ventilated to protect the operators. Operators are also required to wear respirators for certain operations. The

OSHA standard for CS 2 is 10 ppm, and the Tennessee State limit is 4 ppm CS 2 . Ventilation air is vented to and exhausted from the process area surrounding the reactors, spinning machines, stretch rollers, the hot dip step, and the purifying washes. Because rich streams are necessary to achieve significant reduction, the exhaust streams from these areas are very dilute, which affects the recovery efficiency of the condensers.7

Both CS 2 and H 2 S from the hot dip step vent stream are controlled by a condenser (located in a separate building). In this system, water vapors (steam) are condensed out of the vent

stream with a direct-contact condenser and the condensed water is sent to the wastewater treatment system. The remaining CS 2and H 2 S vapors are pulled by vacuum jet to a second

direct-contact condenser. The H 2 S is scrubbed from the gas stream with a cool, weak lye

solution and the CS 2 condenses due to the decrease in temperature. Noncondensibles exit through one of the main stacks. The lye (NaOH) solution and condensed CS 2are sent to a settling tank for separation (by gravity) and the condensed CS 2is piped underground to the submerged CS 2 storage tanks in the water containment pool. The separated lye solution is returned to the condensation system. Another condensation system similar to this system

controls CS 2 and H 2 S emissions from the sluice box. The inlet vent stream temperature and the condenser lye solution temperature are contained in the Confidential Addendum, item 22. The emission reduction achieved by each of these condensers is 99 percent for CS 2 .

Carbon disulfide is emitted through several stacks to the atmosphere (there are four main stacks and several smaller stacks). Two of the main stacks vent the spinning area (spinning machine through the cutters); the other two stacks vent the finishing operations for the rayon fiber. Random sampling has shown concentrations of CS 2in the main stack outlets between 300 to 500 ppm. Information on the main stacks is contained in the Confidential Addendum, item 23.

The facility implemented several modernization projects from 1992 to 1994. The facility has implemented projects to increase the amount of CS 2recovered from the process. Attachment 4 shows the percent recovery from 1991 to 1997. Attachment 4 is contained in the Confidential Addendum. The plant has also established a goal for the ratio of CS 2used per metric ton of fiber produced. Attachment 5 shows the trend for this ratio at the plant. Attachment 5 is contained in the Confidential Addendum. Additional information on CS2 recovery, CS2 usage, equipment changes, and control costs are contained in the Confidential Addendum, item 24.

As part of the plant’s improvement process, a material balance for CS 2usage and emissions has been performed for the entire plant. The plant tracks the total usage of CS 2through its accounting department. The engineering department has determined air flow rates and concentrations (ppm) plant-wide. Plant-wide CS 2material balance data is provided in

Attachment 6. Attachment 6 is contained in the Confidential Addendum.

6. Other CS 2 Control Technologies . Plant personnel have researched a number of potential control technologies for reducing CS 2 emissions to the atmosphere. These control technologies are listed in Attachment 7 and include: (1) condensation, (2) chemical scrubbing, (3) carbon adsorption, (4) catalytic reaction, (5) biological treatment, (6) oil absorption, and (7) incineration. Plant personnel indicated that the ventilation air supplied to some areas of the plant

affects the emission reduction achievable for some control devices. The ventilation air that is

vented to these areas dilutes the concentration of CS 2 . Sending diluted vent streams to an incinerator would require a device that could ha ndle large volumes of flow while also requiring significant auxiliary fuel to maintain combustion temperatures. Diluted streams also are a problem for recovery devices such as condensers where low temperatures are required to get8

significant condensation from the stream. In a ddition to technical concerns, plant personnel have concerns about the cost for environmental controls and indicated that their foreign competitors do not have to make environmental expenditures as U.S. companies do. The technical and economic difficulties for each of the control technologies researched by the company were discussed during the site visit.

Use of condensers to control CS 2emissions has limited applicability for the rayon production plant. A condenser system has been installed for the hot dip step following the spinning operation and for the sluice box prior to the wash track. These systems each achieve 99 percent reduction in CS 2emissions. Because of the large quantity of ventilation air required to reduce operator exposure to CS 2and the dilution of vent streams containing CS 2under the LEL to prevent fire hazards, the majority of vent streams from the process are very dilute. Use of condensation to treat these streams is not economically feasible given the low temperatures required to condense the CS 2 vapor. Condensers are appropriate for high concentration, low

volume vent streams.

Chemical scrubbing has also been examined for scrubbing H 2 S emissions from the spinning and hot dip vents. The H 2 S in the vent stream is removed by contact and reaction with a lye solution. This technology achieves a high removal of H 2 S, approximately 95 percent.

Carbon adsorption has been analyzed as an option for reducing and recovering CS 2 emissions. In this control technology, the vent stream is passed through an activated carbon bed

and the CS 2is adsorbed on the bed. The carbon bed is then regenerated, usually with steam, and the steam and contaminant are condensed and separated. The autoignition temperature of CS 2 is low, and steam desorption can be used, but only when purged in an inert atmosphere such as N 2 . The facility estimates a cost of $44 million to enclose the process equipment, concentrate the vent streams, and purchase and install the carbon bed system. This technology might achieve a 65 percent reduction in CS 2emissions and has the added benefit of recovering the CS 2for reuse in the process (i.e., a cost savings). The plan t has looked at both fixed bed and fluidized bed carbon systems. Problems with this technology in clude bed fires (safety concern), which are more prevalent given the flammability of CS 2 ; the difficulties in regenerating the carbon beds or removing/desorbing the CS 2 from the bed; and the presence of H 2 S in the vent stream, which contaminates the carbon bed (although H 2 S could be stripped prior to the carbon bed).

Use of catalytic reaction to generate H 2 SO 4 from H 2 S and CS 2has been considered. In this system, a two-stage conversion occurs where CS 2and H 2 S are converted to SO 2in the first bed

and converted to SO 3 in the second bed. In a condenser unit, the SO 3 is “wetted out” to generate 98 percent H 2 SO 4 solution. The cost to purchase and install a catalytic reaction unit by Haldor Topsoe is in excess of $30 million and is not attractive given the low cost of H 2 SO 4 compared

with CS 2 . The Haldor Topsoe unit uses a vanadium pentoxide catalyst to promote the reaction; the unit operates at high temperature (800° to 900°C) and is subject to the corrosive nature of the

SO 3 generated. The plant has also looked at a catalytic reaction unit manufactured by German company Kanzler Berfahrenstechnik (vendor is Maurer). The plant estimates that an additional 500 to 600 tons per year of SO 2 will be generated from oxidation of CS 2 . Given the plant’s proximity to Great Smoky Mountain National Park, the National Park Service must approve the9

facility’s SO 2 emissions; however, Lenzing has excess SO 2capacity because current SO 2 emissions from the onsite power plant are less than permitted levels.

The plant has also considered use of a biological treatment system for CS 2 . The vent stream would pass over a bed of peat. The co mpany the plant contacted, Envirogen, indicated that the vent streams are too large and contain too much sulfur for biological treatment to be applicable.

Use of oil absorption has been examined. In this control technology, CS 2is removed from the vent stream by contact with oil absorption liquid in a counter-current packed bed tower. The oil absorption liquid containing the absorbed CS 2is then stripped; the recovered CS 2is condensed and returned to storage and the oil absorption liquid is recycled to the packed bedtower. This control technology is generally applicable for vent streams with higher concentrations. Lenzing has been discussing this option with PPG Industries, who is the CS 2supplier. Analysis of the streams at the Lenzing facility indicate that the most concentrated stream at the facility could possibly be controlled with this t echnology; two of the most dilute streams at the plant were determined not to be candidates for this technology. From a safety and economic standpoint this is the most practical method evaluated to date.

Incineration of the CS 2 and H 2 S has also been analyzed. The plant considered combusting the vent streams in the power plant, which is 1,000 feet from the rayon staple process. The plant would have to pipe the vent stream to the power plant, and there is a fire hazard associated with venting these streams across the facility. In addition, the power plant can handle only a portion of the vent streams from the process. This option has the disadvantage of generating SO 2 emissions, like the catalytic reaction option discussed above, and there are safety concerns.

2 non-CBI Attachments

F:\USER\NPATE\atw_rules\cellulose\lenzing.wpdATTACHMENT 7

CS 2REMOVAL TECHNOLOGIES

• Condensation

• Chemical Scrubbing

• Carbon Adsorption

• Catalytic

Reaction

• Biological

• Oil Absorption

• Incineration