Sector Assessments

An Analysis of Pollution Prevention Opportunities and Impediments in the Pulp and Paper Manufacturing Sector in Georgia

April 1, 1996

Introduction

The purpose of this report is to identify the specific causes of waste generation, and cost-effective solutions that will reduce waste in the pulp and paper industry in Georgia. The benefits of reducing waste are reduced pollution and decreased operating cost to the business. Releases of high-priority toxic chemicals are the primary focus of this report but other significant solid and liquid wastes will be included. Barriers exist that limit the implementation of pollution prevention projects and technologies. Barriers and strategies to overcome them will also be discussed in this report.

Methodology

Review of trade and environmental publications indicated that the processes responsible for Toxic Release Inventory (TRI) releases in this sector are primarily Kraft pulping and bleaching of pulp. Businesses that use these processes were identified by reviewing 1993 TRI reports and the Georgia Manufacturing Directory. There are relatively few pulp and paper mills in Georgia. Telephone interviews were conducted of Kraft pulp mills and paper mills in the state. Visits were made to six mills; various processes related to Kraft pulping, bleaching, and recycling were reviewed. The interviews and plant visits were conducted to collect information on the various types of equipment and chemistries used in the mills. Water usage, pulp production, and information on various other wastes were collected. Mill environmental and production staffs were also questioned about programs at their facilities to reduce waste and evaluate new technologies available to the pulp and paper industry. The results of this study are presented in this document.

Summary

The following key issues were identified as a result of this study 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
• Lime Mud Waste Reduction
• Energy Conservation and Recovery
• Alternatives to Chlorine Bleaching
• Log Yard Waste Reduction

The Georgia Pollution Prevention Assistance Division (P²AD) will assist Georgia pulp and paper manufacturers in addressing these key issues by developing various programs. P²AD will work with existing technical and business organizations to provide training, publication of fact sheets and case studies, and conduct applied research demonstration projects in order to address critical pollution prevention issues.

Profile of the Pulp and Paper Manufacturing Sector in Georgia

Georgia pulp manufacturers produce pulp, bleached pulp, or specialty pulp for the food and pharmaceutical industry. Many of these companies also produce finished paper, paperboard, or linerboard. Twenty-four companies are listed in the Georgia Manufacturers Directory within SIC code 26 that are predominately involved in cellulose pulp manufacturing. Approximately 13,000 people work for these manufacturers. A list of these businesses is provided below in Table 1 with a description of the primary products and number of employees.

TABLE 1 – GEORGIA PULP AND PAPER MANUFACTURERS

Of the 24 manufacturers in Georgia, thirteen are large manufacturers of pulp only, pulp and paper, or pulp and linerboard. These manufacturers produce virgin pulp and form a finished paper product. The pulp may be either bleached or unbleached. Four Georgia mills produce bleached virgin pulp. Pulp is also sold to paper manufacturers that make paper, filter paper, or other specialty paper from pulp. There are approximately 100 companies in Georgia that are primarily paper, paperboard, or paper products manufacturers that do not manufacture pulp. These companies are not the focus of this study.

Another manufacturing group repulps old corrugated cardboard, linerboard, newsprint, and other waste paper. There are at least nine mills producing recycled pulp in Georgia. Recycling mills manufacture pulp for sale to other industries or manufacture a finished paper product. Some recycling mills deink printed stock using floatation or continuous deinking. Bleaching is done primarily with peroxide and less with sodium hypochlorite by recyclers. At least one company recycles newsprint and other paper in a dry repulping process to make insulation, animal bedding, and reseeding material used on highway right of ways.

Paper mills need a source of water and a receiving body to dispose of wastewater. Paper mills are generally located near a river to provide a means of disposal for the often tremendous wastewater stream generated by the mill. A secondary reason is to provide water for mill usage since a number of mills use wells as the primary source of mill supply water. Cooling water is also needed and is usually supplied from surface water. All Georgia mills have wastewater treatment plants except some of the small specialty product mills, and dispose of wastewater directly to a river after treatment. At least one mill disposes of wastewater to a municipal treatment system. Several mills also purchase water from a city or other source of treated water.

Pulp and Paper Industrial Processes

In order to understand the pulp and paper industry, a general description of the pulping and paper making process is needed. Each of the companies uses some or all of these processes.

Wood Yard Operations

Wood is delivered to a pulp mill either as logs or chips. Logs are delivered with the bark attached to prevent loss of moisture and other degradation. Logs are handled in the yard by cranes or log trucks. They are loaded onto a conveyor or log flume where they are carried to a debarker and chipper. Chips are screened to remove over and undersized chips, and then stored in the yard awaiting digestion. The majority of the Georgia virgin pulp mills have wood yards. A growing trend is to eliminate wood yards and receive chipped wood only. Several mills receive only wood chips or are planning wood yard closure in the near future.

Water Treatment

Pulp mills generally require a large amount of water in processing to remove lignin and bleaching byproducts. Water is generally obtained from rivers or wells. From 5,000 to 40,000 gallons of water is required to produce one ton of dry pulp in Georgia’s virgin pulp mills. This water is treated prior to use to remove suspended solids and other contaminants.

Digestion

Chips are heated by steam and white liquor is added. The liquor impregnated chips then enter the digester where they are heated to cooking temperature. Spent cooking liquor or black liquor is removed from the brownstock after cooking. In batch digesters, the brownstock is blown from the bottom of the digester vessel prior to washing. In a continuous digester, washing takes place inside the digester to remove liquor and cool the pulp. In either case, brownstock is washed to remove the majority of spent liquor. It is also screened to remove undigested knots. The majority of the 13 pulp mills use the Kraft process. One mill uses the thermo-mechanical pulping process.

Washing

Pulp washing takes place after each major process. The purpose of washing is to remove undesirable elements from the pulp stream. Black liquor, fines, lignin, and bleach byproducts are removed after each processing step. Washer efficiency can be measured by the cleanliness of the pulp and the amount of water used to achieve that level of cleanliness. There are a number of different types of washers available. Vacuum drum brownstock washers (six-stage or three-stage) were the industry standards up to the 1970s. At least six Georgia mills currently use vacuum drum washers. Pressure brownstock washers represent a later washing technology with at least one mill using this technology. Diffusion brownstock washers are currently the industry standards, but diffusion washers are also being improved upon. Diffusion washers are used by at least three mills. At least two pulp mills in Georgia use Chemi washers, which are the most efficient washers available currently. Each improvement represents cleaner pulp with a water usage reduction.

Refining

Pulp passes through slots in rotating plates to separate the cellulose clumps into fibers and condition the fibers for paper making. Essentially, the fibers are cut to a uniform length during refining which reduces strength. The fibers are also conditioned by refining which improves bonding and strength of the finished paper product.

Oxygen Delignification

Some mills have installed an oxygen stage to further remove lignin from the brownstock as a prebleaching step. Reduced lignin content produces a whiter pulp. Oxygen and white liquor are added to the brownstock in a heated reactor where additional delignification takes place. Lignin compounds freed as a result of oxygen delignification are removed in washing and extraction stages. At least two Georgia mills use oxygen delignification. Oxygen delignification reduces the amount of chlorine or other bleaching chemicals required to whiten the pulp in the bleach stage.

Extended Delignification

Various extended delignification techniques are used to remove more lignin prior to bleaching. Sodium hydroxide (NaOH) and heat act to break complex bonds in the lignin to make them soluble in water or volatile. NaOH and heat also break bonds in the cellulose reducing strength and yield. Extended delignification techniques cook the wood chips at lower temperature for longer periods of time to remove lignin with reduced damage to the cellulose. Several techniques are in use to control temperature and liquor chemistry in the digester. At least four mills in Georgia use extended delignification. Extended delignification reduces the amount of bleaching chemicals required in the bleaching stage to produce the same pulp whiteness.

Bleaching

Bleaching usually takes place in a multistage process. The purpose of bleaching is to remove lignin without damaging the cellulose. One process is the DED process; D represents chlorine dioxide (ClO₂) and E represents extraction. In this process, brownstock is mixed with ClO₂ in the D1 reactor which further reacts with lignin in the pulp. Washing follows to remove the chlorinated lignin compounds from the pulp. NaOH is added to the pulp stream in the E tower and is followed by washing in a press. Extraction neutralizes the pulp and improves subsequent washing. The D2 tower is the last stage of bleaching where ClO₂ provides the final whitening of the pulp. If preceded by oxygen delignification, the process is abbreviated ODED. Chlorine (C), peroxide (P), oxygen (O), sodium hypochlorite (H), and ozone (Z) are other chemicals that can be used in various configurations. For example, ODEoD would consist of:

oxygen reactor > ClO₂ reactor > extraction with oxygen added (EO) > ClO₂ reactor

The final stage of bleaching is often used to whiten or lighten remaining lignin. Eight Georgia mills bleach pulp in some manner, four of which are virgin pulp mills.

Paper Making

The pulp is then transported to the paper machine where a pulp mat is formed on a screen. Water is removed from the sheet by a combination of vacuum, heat, and pressure applied through rollers. The finished paper can be made in a variety of weights and is rolled onto large rollers for shipment to other processing plants. Paper is sometimes coated on the paper machine with kaolin to provide a white surface or has a binder added to increase wet strength. Some binders contain formaldehyde; many companies have replaced these with nonformaldehyde binders. Other coatings and binders contain ammonia or polyvinyl alcohol (PVA). Approximately 17 mills in Georgia produce paper, paperboard, or similar products.

Power Boiler

Energy in the form of heat and steam is generated by burning waste wood from the log yard or fossil fuels. In addition to steam, electricity is also often generated on-site at pulp mills. Pulp and paper mills require a large amount of energy to operate.

Liquor Recovery Cycle

NaOH and sodium sulfide (Na₂S) are the primary pulping chemicals. NaOH reacts with lignin in the wood to release the cellulose fiber. Na₂S buffers the reaction to keep the solution caustic, and aids in the removal of digested lignin by increasing its solubility. Spent cooking liquor, or black liquor contains various organic and sulfur compounds in addition to the reactive pulping components of NaOH and Na₂S. The black liquor is removed from the pulp at various locations after the delignification process and concentrated in an evaporator. The concentrated liquor, or strong black liquor is combusted in a furnace along with sodium sulfate (Na₂SO₄) to recover Na₂S, and sodium carbonate (Na₂CO₃) in the form of ash. This ash is mixed with water and lime (CaO). The resultant reaction forms green liquor and replenishes the original pulping chemicals NaOH and Na₂S; calcium carbonate (CaCO₃). CaCO₃ is precipitated from the green liquor in a clarifier and converted back to CaO in a lime kiln. After removal of CaCO₃, the green liquor becomes white liquor. The recovery cycle consists of a liquor evaporator, recovery boiler, clarifier, and lime kiln.

Wastewater Treatment

Wastewater gathered from various mill processes is treated prior to discharge to reduce biological oxygen demand (BOD), chemical oxygen demand (COD), and total suspended solids (TSS). Wastewater typically passes through a primary clarifier to remove the bulk of the cellulose fibers lost during processing and other solids. Wastewater then passes through aeration ponds to further reduce BOD and COD. Nutrients in the form of ammonium nitrate or ammonia are often added to encourage microbe activity. Wastewater is then discharged directly to a river or tidal river. Wastewater volumes are very large ranging up to 40,000,000 gallons per day with relatively low contaminant concentrations. In addition to BOD, COD, and TSS, color and chlorinated compounds such as dioxin have been of great concern to pulp mills. Aeration and clarification do not significantly reduce color or chlorinated compounds.

Waste Paper Recycling

Another segment of the industry repulps cardboard or newsprint into recycled paper or paperboard. Recycled material is repulped by adding water, sodium hydroxide, and heat. The pulp is then made into a finished paper product on a paper machine in the same manner as a virgin paper mill. Deinking and bleaching are also done at some recycle mills. Floatation is one common method of deinking. Peroxide is commonly used in the bleaching process. Approximately nine Georgia mills are involved in repulping waste paper products.

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