Papermaking

The three stages that are involved in paper making and their purpose are as following:

  • Stock preparation involves processing the pulp into a homogenous slurry with properties suitable for introduction into the paper machine. Mechanical homogenization of pulp, dispersion in water, fiber declustering, introduction of wet additives – used to provide the final paper product with specific desirable properties (such as color and water repellence) and to improve the quality and efficiency of the paper making process–, blending, and contaminant screening are the activities involved in stock preparation.
  • In the wet end of the paper machine, a paper web is formed from the slurry. In the most commonly used Fourdrinier paper-making machines, the slurry first enters a headbox, which creates a uniform layer of slurry and deposits this layer onto a moving fabric (also called wire or forming fabric). This fabric forms the fibers into a continuous web while allowing water removal via gravity and the application of vacuum pressure. Sufficiently dewatered fibers that are beginning to bond to form paper move to the press section of the machine. Here the paper is pressed to remove water and thereby promote further bonding of fibers. As it moves through the press section, the paper is supported by rolls and press fabrics which absorb water from the sheet at the press nips. The bonded and dewatered sheet continues to the dry end.
  • Dry end processes include drying, calendering, and reeling. In the drying section, steam heated rollers compress and further dry the sheet through evaporation, which facilitates additional bonding of fibers. The drying section represents the largest user of energy in the papermaking stage. In calendering the thickness and smoothness of the final paper is controlled by the use of a series of carefully spaced rollers.The drying section represents the largest user of energy in the papermaking stage.

About half of the total steam, electricity, and direct fuel used by the pulp and paper industry is used in paper making. In particular, the drying stage of the paper machine accounts for the vast majority of thermal energy use in papermaking. Most energy saving opportunities for papermaking are therefore related to improving the efficiency of the drying process and recovering its waste heat for beneficial use (Kramer et al., 2009. p..21).

Potential to retrofit paper machines with energy efficiency equipment is limited by the paper machine design (IEA, 2007. p. 201).

PapermakingTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Steam Impingement DryingIf the latent heat from the purge steam is captured, energy savings are estimated to be 10 - 15%. A slight reduction in the electricity consumption is also expected (Martin et al., 2000. p.38).Research
Shoe (Extended Nip) PressAchieveable energy savings through the installation of shoe press range from 2 to 15% depending on product and plant specifications. The application of the X-NIP T shoe press in tissue plants is estimated to reduce drying energy use by 15%(Kramer et al., 2009. p.103).Capital costs have been estimated at $38/ton of paper. Additional maintenance costs are $2.24 /ton of paper(Kramer et al., 2009. p.103).Commercial
Impulse DryingAn estimate has put the possible savings in dry steam utilization at 50 to 75%. Another study reports the energy savings of around 18 to 20% or 2.1 GJ/ton of paper. Electricity requirements increase by 5 to 10% (Kramer et al., 2009. p.112). By allowing 5 to 10 percent points of increased drying, impulse drying can reduce heat energy consumption by 0.44 to 0.9 GJ/t-paper (assuming 2.5 MJ/kg of steam) (BREF, 2010. p 665)Not availableDemonstration
Airless Drying

Approximately 70 - 90% reduction in thermal energy requirements can be achieved. Electricity requirements may increase by (15-20%) due to increased ventilation requirements.

Research
Paper Machine Vacuum System OptimizationAn audit of 14 paper machines at a Canadian paper producer revealed a potential for saving 3.5 MW of power by system modifications and operational changes. That involved even removing some of the vacuum pumps. Cost to achieve initial savings were negligible. Total annual costs savings were about $400,000 per year (2009 dollars). Commercial
Energy Efficient Vacuum Systems for DewateringMills in Europe have realized energy savings between 20 and 45% by installing energy efficient vacuum systems (BREF, 2010. p. 113)Energy related costs savings are between 40 - 46%.Commercial
Thermodyne EvaporatorThe technique reduces drying energy by up to 50%. The technique reduces the emissions through the VOC capture.Commercial
Gap FormingEstimates for the electricity savings are about 40 kWh/ton of paper (Kramer et al., 2009. p.104). A study estimates the cost of installing a gap former with head box to be $75,750/inch of width (1996 dollars) (Kramer et al., 2009. p.104). Commercial
High-Temperature Soft CalenderHigh temperature soft calender which is an improved super calender, reduces the the power requirements to 330 kW compared to the 550 kW for conventional super calender. Commercial
Replacement of Centrifugal Screen with Pressure ScreenWith the use of pressure screen, power consumption was reduced by about 16 kW. The cost of installation of pressure screen is estimated to be Rs. 16 Lakhs. The total annual energy savings from this technique is estimated to be Rs. 6.03 Lakhs. Commercial
Advanced Dryer Controls

In a study performed in a US based mill a potential to reduce steam consumption by around 2 tons per hour was identified with the use of the Dryer Management System™ software tool (Kramer et al., 2009. p.101).

Corresponding energy cost savings of 2 tph steam reduction were $360,000 annually (2006 dollars). Payback period has been estimated as 3 years based on energy savings alone. This period excludes productivity benefits. In another US based mill annual savings of $263 000 were observed due to energy savings enabled with the use of advanced control systems for paper machines (Kramer et al., 2009. p.101).

Commercial
Energy Saving Crown Control RollPower reduction by 42% or 221 kW has been estimated if this technology is applied.Commercial
Elimination of Vacuum for Couch Roll

About 225 kW of electrical power can be saved by replacing suction couch by solid couch and by avoiding operation of holding zone vacuum pump.

The annual monetary savings are estimated to be Rs. 81 Lakhs without substantial investment.

Commercial
Reducing Air RequirementsSavings of 0.76 GJ/t-paper and electricity savings of 6.3 kWh/t-paper are estimated by installing a closed hood and an optimized ventilation system.Investment cost and operation and maintenance cost has been estimated at $9.5/t-paper for closed hood systems and $0.07/t-paper for optimized ventilation system (2000 dollars). Commercial
High Consistency FormingElectricity savings are estimated at 18% which is about 41 kWh/t of paper. Investment cost is estimated as $70/t paper. Maintenance cost is likely to increase by $0.72/t paper. Commercial
Installation of High Efficiency Vacuum PumpsFor a paper machine with six vacuum pumps, a total energy saving of 66 kW (11 kW per pump) was achieved. Total investment cost was about Rs. 3.90 Lakhs. After implementation of new efficient vacuum pumps, annual savings were about Rs. 4.00 Lakhs.Commercial
Optimizing Pocket Ventilation TemperatureIt has been reported that when the temperature of pocket ventilation system can be reduced to between 82 to 90 °C, overall steam consumption in a typical mill can be reduced by around 450 to 900 kg per hour (Kramer et al., 2009. p.102)Paybacks are normally immediate as this technique involves improved operations and control rather than capital investment. Commercial
Hot PressingApplication of steam showers are estimated to reduce the steam requirements by 1 kg of steam per 1 kg paper. Energy savings of about 0.61 GJ/t paper is estimated through hot pressing.Cost for hot pressing technology are estimated to be $26.7/t paper.Commercial
Use of Vacuum Blower Instead of Vacuum Pumps Savings in valuable electrical power is expected.The investment cost required for the vacuum blower was not available.Commercial
Waste Heat Recovery from Paper DryingIn a mill, replacing the dryers with stationary siphons saved 0.89 GJ/t-paper due to enhanced drying efficiency; Steam savings from mechanical vapor recompression system amounts 5 GJ/t-paper (~50%), but increases electricity consumption of 160 kWh/t-paper (Kramer et al., 2009. p.102)Operation cost savings from replacing dryers with siphons amount $0.045/ton paper (1998 dollars). Installation cost of paper machine heat recovery system has been estimated to be around $18/ton paper; By recovering the waste heat from the dryer ventilation and using this for heating the facilities in winter months, a US based mill was able to realize costs savings of $1 000 000 per year. The payback time for the cross-flow heat exchangers installed for this option was 1.5 years (Kramer et al., 2009. p.102). Commercial
Direct Drying Cylinder FiringThe average energy saving is estimated at 1.1 GJ/t-paper (savings will vary depending on the paper type) (Martin et al., 2000. p.31). Additional operation and maintenance costs are estimated at $1.4/t paper. Retrofit costs are high and are estimated to be $111/t paper.Commercial
Gas-Fired Paper DryerGas-fired paper dryer increases the energy efficiency of paper drying.Demonstration
Condebelt DryingReductions in steam consumption are estimated to be 15%, or 1.6 GJ/t-paper, with a slight reduction (~20 kWh/t-paper) in electricity consumption (Martin et al., 2000. p.32).Capital costs are high. Investment cost of $28/ton paper has been estimated for retrofit installations, and $110/t for greenfield plants (1998 dollars) (Martin et al., 2000. p.32). Commercial
Infrared Moisture ProfilingEnergy savings of around 0.7 GJ/t paper and additional electricity requirements of 0.08 GJ/t paper are estimated. Capital investment costs are estimated to be $1.12/t paper.Commercial
High Concentration Size Press

Japanese flag Specific steam consumption is estimated to be reduced by 0.9-1.5 t-steam/t-paper. Given plant production capacity of 400 t/day and operating time 24 hr/day and 330 day/year, reduction of energy consumption by 119,000-198,000 t-steam/year (NEDO, 2008. p. 162).

Japanese flag For a Rod Size Press with 3.3 m width and 1000 m/min speed, equipment cost is estimated to be ¥250 million. Construction cost is approximately ¥50 million (NEDO, 2008. p. 162).

Commercial
Air Impingement DryingIt has been estimated that the impingement drying technique can save up to 10 to 40% steam compared to traditional gas-fired or infrared drying technologies. However electricity consumption increases by 5%.Commercial
Dry Sheet FormingEnergy savings of 5 GJ/t paper are estimated. Increased electricity requirements of about 208 kWh/t paper (Martin et al., 2000. p.33). In Germany a dry forming paper machine with the capacity of 25000 t/y cost $37.6 million in 1997. Installation cost of around $1500/ t paper has been estimated (Martin et al., 2000. p.33). Commercial
Optimization of Water Removal in Press Section

A 7.8 ºC increase in sheet temperature leaving the press provides a 4% decrease in dryer steam (Kramer et al., 2009. p.102).

Commercial
Laser-Ultrasonic Web Stiffness SensorOverall, mill-scale energy savings of 3% have been estimated (Kramer et al., 2009. p.109).Reportedly raw material optimization could save about $200 million in energy costs and $330 million in fiber costs annually in the USA (Kramer et al., 2009. p.109). Demonstration
Pre-treatment of pulp before DryingEnergy savings from this process has been estimated to be 16% of steam or 1.7 GJ/t paper. Research
Optimization of Water Removal in FormingFor every extra unit of energy used to remove one extra unit of water in the forming section, 5 and 25 times the same amount of energy can be saved in the press and drying sections (Kramer et al., 2009. p.101). Commercial
Advanced Fibrous FillersIt has been reported that use of fillers could reduce energy consumption by 25%. Cost savings by $10 to $50/ton of paper have been estimated.Demonstration

Papermaking Publications

Page Number: 

20-21, 100-105