Sector Assessments

Key Pollution Prevention Issues

The following key issues were identified through contacts with Georgia pulp mill personnel, mill tours, interviews with paper industry experts, and review of various trade and environmental publications.

• Lack of Facility Pollution Prevention Programs
• Water Use Reduction and Reuse
• Alternatives to Chlorine Bleaching
• Log Yard Waste Reduction
• Lime Mud Waste Reduction
• Energy Conservation and Recovery

Lack of Facility Pollution Prevention Programs

A number of mills do have formal pollution prevention plans while others do not. Some of the mills are part of wider corporate pollution prevention plans. The goals and methods used are different for each program. Regardless of goals and methods used, the plans should all include waste audits that track waste streams back to the source and estimate total costs associated with the waste streams. Once costs are known, specific projects can be identified that can be justified for their cost reduction potential. Discussions with plant and corporate personnel indicated that many of the plans do not include this basic requirement.

Some of the plans were directed toward long-term technology goals such as zero discharge of wastewater or total chlorine free bleaching. These goals are necessary, but may be realized in 10 or more years. All current paper making technologies will not be replaced with long-term technology changes.

Water Use Reduction and Reuse

Water is used by all pulp, paper, and recycling mills in significant quantity. There are a number of processes which use water and generate waste water, but the primary uses are pulp washing following digestion and bleaching, and deinking and washing in recycling mills. Since most water used by a pulp mill is heated prior to use, reducing water usage can very significantly reduce energy usage. Energy costs and savings are often the most significant aspects of water usage reduction programs.

Brownstock Washing

Pulp washing is usually done in either of four washing systems, vacuum drum, pressure, diffusion, or Chemi. A brief description of each is provided below. Washing is done to remove cooking chemicals and to remove lignin breakdown byproducts as a prerequisite to pulp drying, bleaching, and paper making.

• Vacuum Drum Washing

Vacuum drum washers usually consist of three to six counter-flow stages. Each stage consists of a rotating screen drum which has a partial vacuum applied to the interior. The drum sits in a tank where pulp is diluted with wash water. The vacuum draws a pulp mat against the surface and wash water through the mat. The drum rotation advances the washed pulp mat to the next dilution tank. Wash water discharged from this wash stage is sent to the previous washing stage. At least six Georgia mills use vacuum drum washers.

• Pressure Washing

Pressure washing is similar to vacuum drum, but differs by spraying water under pressure through the pulp mat as the drum rotates. At least one mill in Georgia uses pressure washing.

• Diffusion Washing

Diffusion washing is a counterflow process that takes place in one or more stages. Pulp flow is upward and is carried on a perforated plate; water flow is downward through a series of baffles. This method offers a high degree of cleaning with low water use. At least three mills use diffusion washers in Georgia.

• Chemi or Belt Washing

A Chemi or belt washer is perhaps the simplest washing system design and offers reduced water usage with excellent cleaning. Belt washing is a counter flow process where pulp enters the washer area on a wire belt. Washing takes place under a series of showers. Clean water enters on the opposite end from the pulp and is sprayed vertically through the pulp. The used wash water is then collected and reapplied to the dirtier pulp by the next washing head countercurrent to the direction that the pulp moves. This process is continued through at least seven stages until the wash water is saturated with liquor after washing immediately incoming pulp. The wash water is then sent to the recovery process. Two mills in Georgia are known to use Chemi washers. Reduced dilution of the liquor recovered from washing will result in reduced energy usage in the recovery process.

The effluent from brownstock washing contains black liquor that must be recovered in addition to varying amounts of water. Diffusion washing and belt washing can reduce the amount of water used per ton of pulp in brownstock washing by 50% or more according to published data. However, the mills in Georgia do not show order of magnitude reductions when using the newer washing technologies. Comparison between mills is difficult due to product mixes of virgin and recycled pulp; mills that have replaced vacuum drum washing with diffusion or belt washing report that improved cleanliness or water reductions were achieved with the new technology, but exact figures were not available. Improved cleanliness is important in reducing bleaching load.

Costs of Pulp Washing With a Chemi Washer

Although several mills in Georgia have upgraded pulp washing, specific information on cost and water usage was not available. In the EPA's document, Pollution Prevention Technologies for the Bleached Kraft Segment of the U.S. Pulp and Paper Industry, the following estimate was provided.

Due to the long payback period, replacement of vacuum drum washers with a Chemi washer is more feasible in a new installation or when a new washer is required to replace a vacuum drum washer that has reached the end of its service life. The installation cost does include all support facilities such as a building to house the unit and piping. The actual replacement cost would be less if support facilities were already existing. Also, the operating cost reduction does not include savings in the bleaching stage. Improved washing will result in less lignin in the pulp thus reducing bleaching requirements.

Bleach Mill Effluent Reduction

Washing of brownstock prior to bleaching allows the recovery of wash effluent in the recovery boiler. Once the pulp has gone through a chlorination stage, recovery is not practical due to corrosiveness. Improved washing and increased delignification prior to bleaching decreases bleaching load and reduces the load placed on wastewater treatment. Bleach mill effluent reductions can then best be achieved prior to any chlorination stage. Improved delignification can allow bleached pulp mills to eliminate certain bleaching and extraction stages while achieving the same level of brightness. Elimination of a bleaching stage can reduce water usage by 2,500 gallons per ton of pulp production.

• Bleach Mill Effluent Recycling

Several mills and corporate organizations are exploring reuse or are reusing bleach mill effluent in previous bleaching stages. Bleach mill effluent accounts for approximately 50% of a bleached Kraft mill's water usage with effluent streams from each stage of bleaching. Recycling water to previous stages could reduce water usage by 60% depending upon the bleaching configuration. Wastewater from bleaching and pulping will contain methanol, other organics, and chlorinated compounds. Reuse in uncontrolled areas could increase air emissions. Typically, a mill will recycle white water from the paper machine back through the various bleaching stages in a counter-current process.

Other Water Use Reduction Opportunities

• Process Pump Seals

Seal water used in various pumps has been eliminated by replacing with mechanical face and lip seals in several facilities around the state. Seal water flows are typically not very high, but are continuous and can add up to large volumes over time. Replacing water seals with mechanical seals usually increases energy consumption due to friction. Seal water can also be collected and reused for other processes but may contain contaminants from the chemical passing through the pump.

Seals are also a source of air emissions, water pollution, and raw material loss due to leakage of the material being pumped through the seal. Chemical pump seals are being investigated by some mills for replacement with sealless and magnetically coupled pumps. An example of a sealless pump is a diastolic tube pump. Magnetically coupled pumps transmit power from the motor to the pump with a magnetic field. Traditionally, both designs are better suited for low torque applications. In either case, sealless pumps are not new technology and should work well in the pulp industry.

Union Camp in Savannah has replaced water lubricated seals with mechanical seals. According to an article published in the November 1995 issue of "Pulp and Paper," replacement of braided packing seals with a self-lubricating compound has reduced water usage and equipment failure. The compound used is a "colloidal mixture of lubricants amalgamated with Aragraphe fibers" manufactured by Tom-Pac of Montreal, Canada. The sealing compound also allows leaks to be repaired by injecting more compound into the seal. Replacement of water lubricated seals also reduces the potential of bearing and gearbox contamination with water, and seal water contamination with oil or other materials. Union Camp points out that 95% of the seal replacement projects have been successful. The benefits of this waterless sealing compound to Union Camp have been:

• reduced water usage
• reduced equipment damage
• reduced water contamination
• reduced maintenance time

Vacuum pumps are used to supply vacuum to vacuum drum pulp washers and other mill equipment. Vacuum pumps are typically liquid ring pumps which use water for sealing and cooling. Water usage is continuous and can be high depending upon the size of the pump. Liquid ring vacuum pumps represent the common technology used in hospitals and other facilities needing large vacuum volumes. In resent years, oil-free and oil-flooded rotary screw pumps have been used in some cases to replace liquid ring pumps to reduce water usage in hospitals. This technology may be useful in the paper industry to replace liquid ring vacuum pumps. Water discharged from liquid ring pumps should be suitable for reuse in any number of mill applications, but may contain some process contaminants.

• White Water Recycling

Paper machines can generate significant amounts of wastewater. One mill generated 3,000 gallons per ton of paper. White water is typically clean, but may contain some contaminants such as fiber, lignin compounds, and various organics. Some of Georgia's pulp mills are recycling paper machine water back to bleaching or pulping operations. Where bleaching does not exist, white water from the paper machine can be reused or partially reused directly in pulp washing or in the wet end of the paper machine. One Georgia mill recycling corrugated material reuses all white water after clarification. The sludge that settles during clarification is also reintroduced into the process. The company, Sweetwater Paper discharges approximately 810 gallons per ton of pulp produced.

Alternatives to Chlorine Bleaching

Waste Generation

Wastes of greatest concern from bleaching are chloroform and dioxins. Elemental chlorine and sodium hypochlorite are the two bleaching chemicals most associated with chloroform and dioxin formation. For this reason, most mills have eliminated sodium hypochlorite and replaced chlorine to some degree. Of the six virgin bleached Kraft pulp mills in Georgia, three have replaced elemental chlorine with chlorine dioxide. The other three have substituted varying amounts of chlorine dioxide.

Bleaching, as previously discussed, is a multistage process. Historically, bleaching was considered a separate process from digestion and began with a chlorine stage. Currently, with elemental chlorine use in decline, it is more difficult to define where digestion or delignification ends and bleaching begins. Some of the pollution prevention options discussed below perhaps are closer to delignification than bleaching in historical terms. In either case, the basic purpose of bleaching is to further selectively delignify pulp.

Pollution Prevention Options

• Chlorine Dioxide Substitution

Georgia pulp mills have proven that 100% chlorine dioxide replacement for elemental chlorine is technically and economically feasible. Mills nationally have reported pulp quality improvements by switching to chlorine dioxide. Some mills using less than 100% chlorine dioxide report that increases in substitution rate are not economically feasible. The lack of economic feasibility seems to be related to equipment costs as opposed to chlorine dioxide cost. Replacement or upgrade of washers, bleach tower materials, and chlorine dioxide generators were all mentioned as needed prior to increasing substitution rates at these mills. Full substitution can also cause reduced pulp yield and reduced brightness according to some published data.

Chlorine dioxide costs more than elemental chlorine. Even with chlorine dioxides greater reactivity, chlorine dioxide can cost more than eight times as much as elemental chlorine according to EPA documents. It is estimated by the EPA that the total cost of generating one pound of chlorine dioxide is approximately $0.50. The cost of an equivalent amount of chlorine is $0.06. In a 1,000 ton per day mill operating at 11% substitution, an increase to 50% substitution would cost $5 million initially with an increase in operating costs of $1.9 million annually or $5.40 per ton. Increasing to 100% substitution would cost $15.9 million initially with an increase in operating cost of $7.1 million annually or $20.30 per ton. Considering that pulp prices can approach $1,000 per ton, 100% substitution represents an increase in operating cost of about 2%. These estimates are based on general averages and not one particular mill.

Reducing dependence on chlorine bleach can best be achieved prior to bleaching. Bleaching is basically an extended chemical delignification process. Chlorine is used to selectively delignify pulp without causing the damage to cellulose that traditional pulp digestion causes. The key to reducing chlorine use is to find methods which delignify further prior to the bleaching stage.

• Improved Chip Uniformity

Uniform, thin chips achieve a greater degree of delignification in standard or modified cooking processes by allowing the chip charge to reach a predictable amount of digestion using a specific chemical and thermal mix. Various methods are available and include improved screening and rechipping of oversized chips. This is a lower cost option for improved delignification with or without bleaching.

• Extended Delignification

A number of methods exist for improving delignification without extensive cellulose degradation. At least four mills in Georgia use extended delignification techniques. These techniques are primarily applicable to continuous digesters. New digesters can cost upwards of $15 million. Some Kamyr digesters, which are the most common type, can be refitted at costs reported in the $1 million range. Batch digesters can also be refitted in some cases. Reduced operating cost by refitting results in payback periods of approximately 18 months according to EPA documents. The cost savings are reported to be in steam and reduction in bleach chemical usage.

• Oxygen Delignification

Oxygen delignification requires the addition of a reaction tower between the brownstock washers and bleach plant. Oxygen and sodium hydroxide is added to brownstock. Reduction of bleaching chemistry by 50% can be achieved in the bleaching process if preceded by oxygen delignification. Washing follows oxygen delignification; effluent can be recovered or discharged. At least two Georgia mills use oxygen delignification. Cost of building a new oxygen delignification tower can be in the $10 to $30 million range, but may be offset by reducing bleaching needs. Operating costs have been estimated to decrease by up to $3.70 per ton for softwood and to increase by up to $6.65 per ton for hardwood based on studies conducted in Sweden and published by the EPA.

• Ozone Delignification and Bleaching

Ozone delignification is not used by any Georgia mills; only one full-scale mill operates within the U.S. Ozone delignification is similar to oxygen delignification. The Union Camp mill in Franklin, Virginia, began operation in 1992 with an OZEoD extended delignification and bleaching process at 1,000 tons per day of bleached kraft production. The overall installation cost was $113 million. Operating costs of the OZEoD delignification and bleaching process are reported to be about 50% less when compared to the more conventional CEDED or DEDED process. D represents chlorine dioxide, E represents extraction, O represents oxygen, and Z represents ozone. There is one pilot mill in Georgia capable of ozone delignification and bleaching. The mill is operated by the University of Georgia for the use of the school and industrial customers for research.

• Alternative Chemicals Used in Bleaching

Chlorine and chlorine dioxide are the only bleaching chemicals used in Georgia by virgin Kraft pulp mills. Oxygen and peroxide are used to augment sodium hydroxide extraction. Oxygen and peroxide act to delignify in the extraction stage essentially replacing chlorine in later stages. Sodium hydrosulfite is used by one mill in a bleaching operation producing newsprint. No Georgia mills use ozone in bleaching, although ozone bleaching is used in a pilot mill in South Carolina and a full-scale mill in Virginia.

• Enzyme Bleaching

Enzymes are used by wood eating insects and bacteria to break lignin bonds or to delignify pulp. Xylanase is an enzyme family related to the chemicals secreted by such bacteria; it appears to be useful in pulp bleaching, extended delignification, and deinking. Mills nationally have used this chemical in trial runs; results indicate that up to 50% reductions in chlorine requirements can be achieved without damage to the cellulose. Application of xylanase appears to be simple. Following brownstock washing, xylanase is applied to the pulp as it enters the high density storage tank. Xylanase works in the high density storage tank and requires between 30 and 180 minutes of reaction time. A washing stage follows the xylanase treatment. No Georgia mills report using xylanase, but it appears to be a low cost method of achieving significant results. Other enzymes such as mannanase are being investigated.

• Catalyst Improved Delignification

Anthraquinone

Anthraquinone is a pulping reaction catalyst which was found to increase the speed of pulping, increase yield, and reduce pulping chemical usage by up to 10%. Anthraquinone is one of the few new technological discoveries in the Kraft pulping field. Due to cost, anthraquinone has not been used extensively in the U.S. except in testing. Approximately 100 mills worldwide use anthraquinone. Although developed as a pulping pollution prevention technology, it may have greater use and be more cost effective if used as an aid to extended delignification. The cost of anthraquinone is expected to drop in the near future due to patent expiration. Renewed interest may develop as a result. Anthraquinone has been estimated to increase pulping costs by approximately $5.00 per ton, but with increased yields of 0.75% and reduced recovery boiler loading. An increase yield of 0.75% represents an increase in production of 7.5 tons per day in a 1,000 tons per day mill.

Polysulfide

Polysulfide is another catalyst mentioned in trade magazines applicable in pulping. Yield increase of 1.5% are possible with improvements in strength. It is possible to use both anthraquinone and polysulfide together. TAPPI publications report that yield increases of approximately 2.5% are possible.

Lime Mud Waste Reduction

Waste Generation

Lime mud waste is directly related to lack of lime kiln capacity. Some mills dispose of up to 200 tons per day. Lime mud disposed of must be replaced by purchasing calcium oxide. Disposal and purchase increase operating cost and fill landfills. There is some offsite reuse of lime mud, but the majority is disposed in landfills or storage lagoons.

Characteristics of Lime Kilns

Lime kilns are typically long rotating tubes where combustion gasses and calcium carbonate pass through changing calcium carbonate to calcium oxide and carbon dioxide. Heat loss is great since insulation is difficult to apply to the rotating housing. Downtime is one reported additional problem. For various reasons such as mechanical failure, kilns are often offline. Since pulp mills operate continuously, lime mud produced during kiln downtime is often landfilled.

Pollution Prevention Options

• Install Second or Larger Lime Kiln

Some mills have increase kiln capacity by adding second kilns. In some cases, Georgia mills have reclaimed tons of lime mud stored in treatment lagoons after adding kiln capacity. Kilns are high cost devices. The economics of installing a new kiln are not known.

• Vertical Kilns

Vertical lime kilns can offer reduced down-time, improved energy efficiency, and larger kiln capacity in a smaller footprint area. Vertical kilns have not traditionally been used due to some manufacturing limitations. A NICE3 grant was awarded to Altex Incorporated to develop a vertical lime kiln; the pilot plant tests are targeted to Weyerhaeuser's Flint River Plant in Oglethorpe, Georgia. More information is contained in Appendix II.

Energy Conservation and Recovery

Waste Generation

Energy is heavily used by the pulp and paper industry. Most mills generate steam and electricity by burning black liquor, coal, wood, and natural gas. Coal combustion is responsible for much of the sulphuric acid and sulphur dioxide emissions reported on the TRI. Additional expense to pulp mills in treating exhaust stack emissions is also incurred. Ash is also a significant solid waste stream and disposal problem when burning coal or wood waste.

Characteristics of Energy Generation in Georgia Mills

Mills typically burn wood both as an energy source and disposal method to reduce volume. Mills that cannot meet their energy needs from wood waste and black liquor combustion purchase additional fuel in the form of wood, coal, bark, fuel oil, and natural gas. Some mills have chosen to only burn wood since it is a low sulphur fuel source. Many mills generate excess electricity to sell back to utility companies or participate in the utilities' power grid load management program. This can be a good source of revenue for some mills. The majority of energy is used to generate steam to heat water, processes, or generate electricity.

Pollution Prevention Options

Sulphur emissions and ash generation can be reduced by burning less fuel. Less fuel will be burned if the energy demand of the mill is reduced, and energy value of the fuel is maximized.

Since water is generally heated prior to use in mill operations, water usage reduction will reduce energy costs. If a heated water flow at 180 F is reduced 100 gallons per minute, the annual water reduction is 50,400,000 gallons. The energy reduction assuming 65 F ambient is 46,368,000,000 BTU. Assuming that water costs $2 per 1,000 gallons, water costs will reduce $100,800. Energy costs will reduce $289,336 assuming an energy cost of $6.24 per million BTU.

Energy demand can be lowered in pulp and paper mills by capturing and reusing waste heat. Energy lost through cooling towers, exhaust stacks, wastewater, and product can all be recovered for reuse. Heat recovery and utilization opportunities vary at each mill depending upon the mill age and layout. One mill in Georgia has identified several recovery opportunities. In this one mill specific example, recovery of heat from wastewater by installing liquid-to-liquid heat exchangers to heat incoming process water was estimated to cost approximately $1 million for installation with a payback of less than two years.

Energy requirements can be lowered by using more efficient equipment such as high efficiency electric motors or by redesigning processes. For example, energy required for drying can be reduced by decreasing water content of pulp before drying.

Pollution Prevention Recommendations for Reducing Energy Usage

A complete energy assessment should be conducted at each facility to identify opportunities. Oglethorpe Power and Georgia Power, the primary suppliers of electricity in Georgia, both will conduct very thorough audits complete with recommendations and cost / benefit estimates. The Energy Analysis and Diagnostic Center (EADC) of Georgia Tech's Economic Development Institute also performs advanced energy audits. EADC can be contacted by calling (404) 894-3844. Some of the common opportunities identified through audits are:

Specific recommendations will vary at each mill location.

The energy value of wood chips can be increased by decreasing moisture content. Moisture content will increase in chips stored in piles outdoors. Placing a cover over chip and bark fuel piles is one method of reducing moisture, increasing energy value, and decreasing decay. Mills will sometimes store pulp chips in silos; this would be a good storage method for fuel as well. Turning chip piles is another method of decreasing decay and moisture content. Energy values can increase 10% or more by decreasing moisture content, with a resulting 10% reduction of ash, fuel demand, and some air emissions.